Method of producing a laminated structure

ABSTRACT

A method of laminating a structure comprises at least two layers and a photopolymerizable adhesive composition between the layers, at least one of the layers being opaque, colored, or reflective. One or both of the layers is transmissive to actinic radiation in wavelengths in the range of greater than 400 nm and up to 1200 nm. The photopolymerizable adhesive composition absorbs radiation in the identified spectral region of the radiation transmissive layer. Curing is effected by directing radiation in the identified spectral region through the radiation transmissive layer and produces a laminated structure. 
     An underfilled flip chip assembly on an integrated circuit board substrate can be prepared by the method described above. The photopolymerizable adhesive composition can be applied directly to one or both surfaces of an aligned integrated chip and circuit board substrate or the chip aligned on an integrated circuit board substrate can be capillary underfilled with the photopolymerizable adhesive composition, which is subsequently cured. Data storage disks can also be prepared by the method of the invention.

This is a divisional of application Ser. No. 09/365,289, filed Jul. 30,1999, now U.S. Pat. No. 6,395,124.

FIELD OF THE INVENTION

This invention relates to a method for laminating layers or articles,the method comprising curing a photopolymerizable composition through acolored, opaque, or reflective substrate. The article can be, forexample, an electronic component, a printed circuit board, or the layerscan be two opposing faces of a compact disc.

BACKGROUND OF THE INVENTION

Photopolymerization of monomers using UV light to prepare adhesivecompositions is an established part of polymer chemistry. Numerousphotopolymerizable compositions, for example, those comprisingethylenically-unsaturated monomers and at least one photoinitiator, havebeen photopolymerized using UV irradiation. A necessary condition forthese photopolymerizations is that the photopolymerizable compositionsmust be directly exposed to the UV irradiation in order for thephotoinitiating component to generate the free radicals required toinitiate the photopolymerization process. Numerous industrial processesrely on selective UV photopolymerization, wherein a mask is used toblock UV irradiation to specified areas of a surface or substrate sothat photopolymerization takes place only in the exposed areas.

In the electronics industry, numerous methods have been used to bondelectronic components together for purposes of forming multilayercomponents or simply adhering a component to a substrate. Methodsinvolving photopolymerization have generally been limited to situationswhere at least one of the substrate or the component is essentiallytransparent to UV irradiation. However, in the case of bondingcomponents to a printed circuit board (PCB), this seldom is possible,since PCBs are often made of opaque and colored materials and theyusually are at least partially covered with metallic circuit traces. Inaddition, the electronic component itself, e.g., a chip, typically iscompletely non-transmissive to electromagnetic radiation. In general,the electronics industry has turned to thermally polymerizable adhesiveswhen reinforcement of solder bonds is desired. This is not entirelysatisfactory because of the lengthy thermal curing cycles required. Inaddition, some electronics components may be heat sensitive andfree-radical thermal polymerizations in general do not lend themselvesto patterned or selective activation.

Photopolymerization has been used in the bonding of electroniccomponents. For example, surfaces to be joined have been coated with aphotopolymerizable adhesive, followed by irradiating the adhesive, thenplacing the two parts together and allowing the irradiated adhesive tocompletely cure. Alternatively, irradiation at the peripheral edges ofparts to be joined can result in a bond of sufficient strength totemporarily hold a component in place. Often, heating the joinedcomponents is necessary for complete curing.

Curing of photopolymerizable adhesives by UV irradiation through asubstrate is known. For example, DE 3939628 discloses bonding ofelectronic components to aluminum oxide or aluminum nitride ceramicsubstrates that are up to 1500 μm thick by UV irradiation of at least 50mW/cm output density. Transmission of UV light through an aluminum oxideceramic substrate of 1016 μm thickness is reported to be about 0.6%.

U.S. Pat. No. 4,656,314 discloses curing of a conductive metal-coatedUV-curable ink on a translucent PCB by UV irradiation from both the topand bottom of the PCB, wherein at least some of the UV light passesthrough the substrate from the underside to assist in the completecuring of the ink. The substrate is characterized as a sheet ofpolyester or polycarbonate that must be at least partially translucent,preferably more than 50% translucent to UV light. Conventional printtreated MYLAR (Dupont) is described as an effective commerciallyavailable substrate.

U.S. Pat. No. 5,065,505 discloses a method of connecting circuit boardswherein a photocurable adhesive is coated onto a light-transmissivecircuit board on which electrodes have been formed. Light is irradiatedthrough the circuit board from the side opposite the coated side, curingthe adhesive in areas not shaded by the electrodes. Exemplifiedphotoinitiators have absorption peak wavelengths ranging from 240 nm to365 nm. Photoinitiators useful in the visible light range are notdescribed. Suitable circuit board substrates include polyimide resin,polyester resin, and the like.

Japanese Kokai Application JP 7-106723 discloses curing of adhesivesthrough a flexible circuit board that is transmissive to 5% or more UVlight having a wavelength between 350 and 400 nm. Base films, throughwhich UV-curing takes place, can include poly(etherimide),poly(ethersulfone), polyethylene naphthalate, polyether ether ketone,polycarbonate, and polyethylene terephthalate.

Japanese Examined Application JP 7-81114 discloses curing aphotohardenable adhesive in the presence of a diketone photoinitiatorand a dialkylamino benzophenone photosensitizer by irradiation through asemitransparent substrate using irradiation wavelengths up to 436 nm.

U.S. Pat. No. 5,607,985 discloses a photopolymerization initiator forvisible-light polymerizing adhesives comprising a photopolymerizationinitiator, an aliphatic tertiary amine and a radical polymerizingmonomer. Adhesion of a sandwich construction comprising two opaque glasspieces, each having 10% light transmissivity at 510 nm and 0% lighttransmissivity between 490 and 200 nm, on exposure for two minutes to ametal halide lamp, is described.

U.S. Pat. No. 5,798,015 discloses generating reactive species(adhesives) by providing a wavelength-specific sensitizer in associationwith a reactive species-generating photoinitiator and irradiating thewavelength-specific sensitizer. The method is used to laminate at leasttwo layers together by coating the adhesive between the layers andirradiating to effect polymerization thereof, providing that at leastone of the layers is a cellulosic or polyolefin nonwoven web or film andthe sensitizer is one of a set of specified arylketoalkene moieties.

Optical recording discs, such as compact discs and CD-ROMs, oftencomprise two or more layers of a polymeric base substrate, each of whichcomprises a recording layer, bonded together by an adhesive with bothrecording layers facing each other. Typically, the recording layerscomprise an opaque metal foil. Uniform curing of the adhesive betweenthe foils is difficult. U.S. Pat. No. 5,360,652 discloses such anoptical recording disc, wherein the adhesive is a photocurable adhesive.In order to adhere the two discs together, the recording medium isconfigured not to extend to the periphery of the discs so that UVirradiation rapidly cures the adhesive around the edges of the disc,allowing the masked adhesive under the recording medium to cure only bycontact with initiators in the irradiated region.

U.S. Pat. No. 5,785,793 discloses one- or two-sided irradiation of anoptical recording disc having one or two back-to-back storage mediumlayers. Curable adhesive is used on the side opposite from the recordingmedium, in either case, so that UV irradiation must pass through atleast the recording medium in order to cure the adhesive. Heatmanagement is an issue for optical recording disc manufacture, since thediscs are easily warped and the recording medium is typically alow-melting metal, such as aluminum. Xenon flash lamps are preferred forirradiating the curable adhesive and bonding the discs together.

Bonding of DVD (Digital Versatile Disk) substrates is described by D.Skinner, “UV Curing Through Semi-transparent Materials—The Challenge ofthe DVD Bonding Process,” RadCure Letter, April, 1998, p. 53-56, whereinUV light of 320-390 nm wavelengths is shown to penetrate a 40 nm thickcoating of aluminum on a polycarbonate substrate with 91%transmissivity. Curing of an adhesive under these conditions is notdisclosed.

SUMMARY OF THE INVENTION

Briefly, the present invention provides a method of laminating astructure comprising the steps of:

a) providing a structure comprising at least two layers and aphotopolymerizable adhesive composition between the layers,

1) at least one of the layers being opaque or colored and transmissiveto actinic radiation in an identified spectral region having one or morewavelengths greater than 400 nm and up to 1200 nm, the layer beingessentially free of cellulosic and olefinic functionality,

2) the photopolymerizable composition comprising a photopolymerizablemoiety and a photoinitiator therefor that absorbs actinic radiation inthe identified spectral region of the radiation transmissive layer, thephotopolymerizable moiety being polymerizable in a hydrosilation,cationic, or free radical polymerization process, with the proviso thatthe free radical polymerization process is free ofdialkyaminobenzophenone sensitizer,

b) directing actinic radiation within the identified spectral regionthrough the radiation transmissive layer and into the photopolymerizablecomposition for less than two minutes to cure the photopolymerizablecomposition,

whereby the resulting polymerized composition adheres to the layers andprovides a laminated structure.

Optionally, the structure, including the photopolymerized composition,can be heated to complete the polymerization of the photopolymerizablecomposition.

Each of the layers of the invention independently can be a coating, afilm, or a substrate, or it can be included in an article. Preferablythe article can be an electrical component such as an integrated circuitchip (IC) or a printed circuit board (PCB).

In another aspect, there is provided a method for identifying suitablematerials for two layers, a photopolymerizable adhesive composition, anda radiation source to be used for producing a laminated structure, themethod comprising the steps of:

a) identifying two layers, at least one of which is colored, opaque, orreflective and is transmissive to actinic radiation in an identifiedspectral region having one or more wavelengths greater than 400 nm andup to 1200 nm, with the proviso that when the radiation transmissionlayer is colored or opaque, it is essentially free of cellulosic andolefinic functionality,

b) identifying a photopolymerizable composition to be disposed betweenthe layers comprising a photopolymerizable moiety and a photoinitiatortherefor that absorbs radiation in the identified spectral region of theradiation transmissive layer,

c) identifying a radiation source that provides actinic radiation in theidentified spectral region of the radiation transmissive layer and inthe light absorbing wavelengths of the photoinitiator,

whereby directing the actinic radiation, on demand, through the colored,opaque, or reflective layer, for a time sufficient to effectpolymerization of the photopolymerizable composition, produces alaminated structure.

In a further aspect, the present invention provides a method forpreparing a soldered and underfilled flip chip assembly on a circuitsubstrate, the method comprising the steps of:

a) providing

1) an integrated circuit chip having a surface comprising reflowablesolder bumps with contact tips thereon, and

2) a printed circuit substrate having a bonding site,

wherein at least one of the chip and the circuit substrate istransmissive to actinic radiation in an identified spectral regionhaving wavelengths greater than 400 nm and up to 1200 nm,

b) applying a photopolymerizable adhesive composition directly to one orboth of the surface of the chip with solder bumps and the bonding siteof the printed circuit substrate, the method providing exposure of thecontact tips of the solder bumps of the chip, the photopolymerizableadhesive composition comprising a photopolymerizable moiety and aphotoinitiator therefor, wherein the photopolymerizable compositionabsorbs radiation in the identified spectral region of the radiationtransmissive chip or circuit substrate,

c) aligning and pressing the exposed tips of the bumps on the surface ofthe chip against the bonding site of the circuit substrate,

d) melting and reflowing the solder to establish electrical contactbetween the chip and the circuit substrate, wherein thephotopolymerizable material remains substantially uncured, and

e) directing radiation within the identified spectral region through theradiation transmissive chip or circuit substrate for a time sufficientto cure the photopolymerizable adhesive composition and to produce thesoldered and underfilled flip chip assembly on the circuit substrate.

Optionally, a functional evaluation of the soldered electricalconnections may be performed prior to irradiation as described in stepe). If the evaluation shows insufficient electrical contact between thechip and the substrate, the assembly can be reheated to allow easyremoval of the chip from the substrate, after which the chip and thebonding site can be cleaned, soldering can be repeated, and a functionalevaluation repeated to assure adequate electrical connection prior toirradiation.

In a still further aspect, the present invention provides a method oflaminating a structure comprising the steps of

a) providing a structure comprising at least two layers and aphotopolymerizable adhesive composition between the layers,

1) at least one of the layers being one or both of a reflective layerand a layer incorporated in an electronic component that is transmissiveto actinic radiation in an identified spectral region having one or morewavelengths greater than 400 nm and up to 1200 nm,

2) the photopolymerizable composition comprising a photopolymerizablemoiety and a photoinitiator therefor that absorbs actinic radiation inthe identified spectral region of the radiation transmissive layer, thephotopolymerizable moiety being polymerizable in a hydrosilation,cationic, or free radical polymerization process,

b) directing actinic radiation within the identified spectral regionthrough the radiation transmissive layer and into the photopolymerizablecomposition for less than 2 minutes to cure the photopolymerizablecomposition,

whereby the resulting polymerized composition adheres to the layers andprovides a laminated structure. In a preferred embodiment, this methodprovides a data storage disk.

In a yet further aspect, the present invention provides a method forpreparing a soldered and underfilled flip chip assembly on a circuitsubstrate, the method comprising the steps of:

a) capillary underfilling a soldered chip on an integrated circuitsubstrate with a photopolymerizable adhesive composition comprising aphotopolymerizble moiety and a photoinitiator therefor,

wherein the circuit board is transmissive to actinic radiation in anidentified spectral region having wavelengths greater than 400 nm and upto 1200 nm, and

wherein the photopolymerizable composition absorbs radiation in theidentified spectral region of the radiation transmissive circuitsubstrate, and

b) irradiating the circuit substrate from the side opposite the sidebearing the soldered chip with actinic radiation in said identifiedspectral region.

In this application:

“actinic radiation” means photochemically active radiation and particlebeams, including, but not limited to, accelerated particles, forexample, electron beams; and electromagnetic radiation, for example,microwaves, infrared radiation, visible light, ultraviolet light,X-rays, and gamma-rays;

“cure” and “polymerize” are used interchangeably in this application toindicate a chemical reaction in which relatively simple moleculescombine to form a chain or net-like macromolecule;

“colored” means having visually perceptible color either to the naked orunaided eye, or to the aided eye, e.g., the light visually perceived bythe eye after shining a light on a substrate;

“DVD” means both Digital Video Disc and Digital Versatile Disc;

“UV” or “ultraviolet” means actinic radiation having a spectral outputbetween about 200 and about 400 nanometers;

“visible light” means actinic radiation having a spectral output greaterthan about 400 to about 700 nanometers;

“near IR” or “near infrared” means actinic radiation having a spectraloutput between about 700 and about 1200 nanometers;

“transparent” means that the material, when viewed under an opticalmicroscope, (e.g., with a stereoscopic microscope at 50× and underoblique or transmitted light), has the property of transmitting rays ofvisible light so that images of articles viewed through the materialhave sharp edges;

“translucent” means that the material, in whole or in part (asd whenpatterned), when viewed as described under an optical microscope, hasthe property of transmitting visible light to some degree so that imageshave unclear or blurred edges;

“opaque” means that the material, when viewed as described under anoptical microscope, has the property of being impervious to radiation ata given wavelength, in a multilayered material, one or more layers havecontinuous or discontinuous opaque regions; curing takes place throughthe opaque regions;

“light transmissive” means a substrate or article having an opticaldensity of 4.0 or less, preferably an optical density between 4.0 and2.0, and more preferably having an optical density between 4.0 and 3.0when irradiated with a light of wavelength greater than 400 to 1200nanometers;

“reflective” means capable of bending or returning or throwing back atleast 90% of the incident light from a surface irradiated by that light;

“group” or “compound” or “ligand” means a chemical species that allowsfor substitution or which may be substituted by conventionalsubstituents which do not interfere with the desired product, e.g.,substituents can be alkyl, alkoxy, aryl, phenyl, halo (F, Cl, Br, I),cyano, nitro, etc.;

“photopolymerizable moiety” means a photopolymerizable monomer,oligomer, or polymer; and

“reflow” means melting of a solder.

The present invention is advantageous in that it provides a uniquemethod for laminating layers or articles using a photopolymerizableadhesive composition. The adhesive can be cured on demand indirectlythrough a variety of colored, opaque, or reflective substrates usingactinic radiation in the range of greater than 400 to 1200 nm.

The curing can take place at elevated or ambient (20-25° C.)temperatures, which can be advantageous for temperature sensitivesubstrates.

Conventional methods of adhering face-down integrated circuits (e.g.,flip-chips), or other articles, to ceramic, polyimide or epoxy-filledprinted circuit boards (PCB's), or other substrates, typically usethermally cured epoxy-based adhesives which can be applied withcapillary action after a solder connection has already been established,when reinforcement is necessary. This becomes increasingly difficult as,for example, chip size increases and as the number of electricalconnections per chip increases. Also, there is a need in the art forpre-applied low temperature, e.g., less than 50° C., cure-on-demandadhesives and that do not use UV activated systems. UV activated systemscan be impractical due to their inability to transmit UV light eitheredgewise or through an epoxy PCB or other substrate. Prior art UVmethods traditionally required colorless transparent substrates. Thepresent invention method, comprising photocuring using visible ornear-infrared light, is advantageous in that colored and opaquesubstrates can be used. It is advantageous, also, that UV absorbing orreflecting substrates that are transmissive to actinic radiation withinthe desired spectral range can be used in the present invention method.Further, it is desirable to prepare wafers or circuits havingpre-applied, self-fluxing, curable adhesives applied to the underside(e.g., bumped side) of the chip or circuit. Also, rapid cure of theadhesive is desired in order to minimize production time.

The present invention overcomes deficiencies of conventional curingsystems by providing a method to rapidly photopolymerize a variety ofradiation curable compositions (both thermoplastic films and flowableresins) directly through various PCB's or other substrates, both inunmetallized and metallized regions of the PCB's or other substrates,using visible light and/or near infrared curing systems. The ability tocure through the back side of a circuit substrate depends on severalfactors including line width and spacing, angle of irradiation,substrate and circuit thickness, and the type of metallized tracing. Thelow temperature method of the present invention can be useful withtemperature sensitive substrates. Any composition that can bepolymerized or crosslinked via direct photolysis or indirectphotochemical generation of a thermal catalyst or initiator can be usedin this approach. Shelf-stable, premixed compositions can be cured ondemand using the method of the present invention.

The present invention is also advantageous in that it allows the use ofa variety of light sources for initiating photopolymerization reactions,including many conventional, non-specialized light sources, such ashalogen bulbs or other sources of visible light and/or near infraredradiation. The method of the invention is thus inherently safer to ahuman user than methods using, e.g., ultraviolet light, since lessvisible light and/or near infrared radiation is required to produce anequivalent amount of light density. The use of visible light and/or nearinfrared radiation sources is also advantageous over ultraviolet lightsources because of the known degradative effects of UV light onsubstrates such as polymers. Finally, the invention allows facilevisible-light curing of photopolymerizable compositions comprisinghelpful ultraviolet absorbing additives such as UV stabilizers andantioxidants.

U.S. application Ser. No. 08/986,661, filed Dec. 8, 1997, which isincorporated herein by reference for its disclosure of flip-chipassemblies and processes including all Figs. of the Drawing, relates toa method and assembly for connecting an integrated circuit chip to acircuit substrate.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1A shows a flip chip assembly, unfilled.

FIG. 1B shows a flip chip assembly, partially underfilled withphotopolymerizable adhesive.

FIG. 1C shows a flip chip assembly, completely underfilled withphotopolymerizable adhesive.

FIG. 1D shows a completely underfilled flip chip assembly exposed tovisible light to achieve curing of the photopolymerizable adhesive.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

The present invention method provides a means to bond, quickly andconveniently, many different articles to a variety of substrates usingactinic radiation in the visible or near infrared range. In somesituations it may be desirable for both substrates to be transmissive tovisible or near infrared radiation, but this is not required.

In a preferred embodiment, the present invention provides a process andassembly to configure a wafer-applied, self-fluxing, underfillphotopolymerizable adhesive resin which can remain essentially uncuredthroughout the entire solder reflow process. After reflow and optionalsubsequent evaluation of electrical function, application of heat inconjunction with an appropriate visible-wavelength light applied throughthe backside of the printed circuit board can be used to provide a veryrapid cure on demand. This can provide an adhesive resin that acts as a‘no-clean’ flux, i.e., washing or cleaning of the PCB is not requiredafter flux. In a single set of process steps, literally hundreds ofchips can be adhered at one time.

The purpose of the flux is to remove metal oxides from the surfaces ofthe solder and the traces on the circuit board in order to permitcomplete wetting of the solder to the traces during reflow. This fluxingaction takes place immediately prior to melting of the solder. In atypical conveyor-based solder reflow oven, the total soldering operationusually takes place over a period of about three to six minutes. Theactual reflow of the solder normally occurs during the last minute or soof the process at which time the temperature of the components can reach220° C. (for eutectic Sn/Pb solder). During most of the time in theoven, however, the temperature of the components is maintained at about140 to 160° C. and it is at this time that the fluxing action takesplace.

An ideal scenario can be as follows: An underfill photopolymerizableadhesive resin with fluxing activity is pre-applied to a chip at thewafer level. The chip is aligned and tack-bonded face-down on a circuitboard assembly, and the board is placed in a conveyor-based reflow oven.While in the oven the circuit board assembly can be heated to atemperature of about 160° C. during which time the adhesive melts. Theboard assembly can then be held at about 160° C. for a period of 3minutes during which time the adhesive acts as a flux and removes metaloxides from the solder and circuit trace surfaces. At this point theadhesive remains completely uncured and possesses low viscosity. Nextthe board assembly is heated to a temperature of 220° C. for a period ofup to one minute, during which time the solder melts and wets out ontothe cleaned surface of the circuit trace. At this point, if a heatcurable adhesive is present, it will begin to polymerize. It isimportant, however, that the viscosity of the adhesive remains low atleast until the solder wetting is completed. In fact, it is actuallydesirable that the adhesive resin remain ungelled after the reflowprocess. Use of a photopolymerizable adhesive resin in the presentinvention achieves these goals. This way, the soldered assembly can beevaluated electrically and if found to be non-functional it can beeasily de-bonded, re-worked, and re-bonded. The need for re-workabilityis very important in many flip chip assemblies because often the circuitboard assemblies are complex and expensive.

It is known in the art that the most effective fluxes are acidic. Forexample, most resin fluxes have pH values between 3 and 5. Inparticular, the active components in most commercial fluxes containcarboxylic acid functionality. This poses a potential problem becauseunderfill adhesive materials are almost always epoxy-based. This meansthat an acidic material possessing fluxing activity which is added to anunderfill adhesive composition will tend to act as a curing agent for aheat curable adhesive resin, thereby making it difficult to maintain lowviscosity until after solder reflow.

In the present invention, however, the wafer-applied, self-fluxingunderfill adhesive resin, being photopolymerizable, can remain partiallyor totally uncured throughout the entire solder reflow process describedabove

Details of processes and materials for achieving flip chip assembliesare disclosed in U.S. application Ser. No. 08/986,661, filed Dec. 8,1997, incorporated herein by reference. A typical assembly process forflip-chip assembly involves the following steps: 1) flux paste isapplied to the substrate bond pads; 2) the IC is aligned and placed onthe substrate while tackiness in the flux holds the chip in place; 3)the assembly is passed through the reflow oven and the solder melts andbonds metallurgically with the substrate pads; and 4) the sample ispassed through a flux cleaning operation.

The finished flip chip assembly must then maintain electrical continuitythroughout the lifetime of the device as measured by accelerated testssuch as thermal cycling and thermal shock. Mismatches of both thecoefficient of thermal expansion (CTE) and the elastic modulus (E)between the silicon IC and the PCB generate high stresses in the contactjoints when the circuit is passed through thermal excursions. Thesestresses can lead to solder joint fatigue failure after repeatedtemperature cycles, and this is a primary failure mechanism for flipchip joints. This mechanism has limited the selection of substratematerials mainly to ceramic hybrid substrates such as Al₂O₃, which hashigh modulus and low CTE, properties similar to silicon. Even withceramic substrates, flip chip assembly is limited to applications withsmall die.

During the last ten to fifteen years there has been increasing interestin learning how to apply this flip chip assembly to both larger size dieand also to a broader range of printed circuit substrates. Specifically,the increased wiring densities available with today's organic basedsubstrates makes them suitable low cost substitutes for ceramicsubstrates. However, the relatively high CTE of organic materials hasslowed the implementation of flip chip assembly on organic substratesdue to the aforementioned failure mechanism. An important breakthroughhas been the development of underfill process. Underfill process uses ahigh modulus curable adhesive to fill the empty space between the solderballs under the chip so that the stress in the joint is shared by theadhesive and distributed more evenly across the entire interface asopposed to being concentrated at the perimeter balls. The use of anunderfill adhesive as described above has enabled a flip-chip technologyto be applied to a broader range of assemblies.

The present invention provides an advance in the art in that theunderfill adhesive resin is photopolymerizable and allows forreworkability of the assembly after evaluation of electrical functionsubsequent to solder reflow and prior to cure of the adhesive.

FIGS. 1A, 1B, and 1C, and 1D show flip chip assembly 10 of the inventionhaving an integrated chip (IC) 12 and a printed circuit board (PCB) 14wherein the IC 12 and PCB 14 are aligned at solder bumps 16 and bondpads 18. In FIG. 1A, IC 12 and PCB 14 are held in alignment by a fluxpaste, not shown. In FIG. 1B, flip chip assembly 10 is shown partiallyunderfilled at the interface between IC 12 and PCB 14 withphotopolymerizable adhesive 24 which has been wicked in position usingapplicator 22. In FIG. 1C, flip chip assembly 10 is shown completelyunderfilled at the interface between IC 12 and PCB 14 withphotopolymerizable adhesive 24. In an alternative embodiment,photopolymerizable adhesive 24 is applied to one or both opposingsurfaces of IC 12 and PCB 14 prior to alignment of IC 12 and PCB 14. Thetips of bond pads 18 and solder bumps 16 are free of adhesive at thetime of alignment of IC 12 and PCB 14 and cure of photopolymerizableadhesive 24. Adhesive can be removed from bond pads by, for example,ablating, abrading, etching, or dissolving. In FIG. 1D, flip chipassembly 10 is irradiated by visible or near infrared radiation 28through PCB 14 so as to produce photopolymerized adhesive 26.

Alternatively, a photopolymerizable adhesive, such as aphotopolymerizable epoxy resin composition, can be introduced under analready-soldered flip chip assembly by any useful method, such aswicking or capillary filling, then photopolymerized in place by themethod of the invention.

Other layers and articles that can be laminated using the method of thepresent invention include, for example, electronic components tosubstrates such as printed circuit boards or flexible printed circuits.Also useful are bonding steps such as board-to-board lamination,lamination of metal circuits or traces, assembly of connectors such asfiber optic connectors, or assembly of articles composed of metallizedsubstrates such as data storage disks including compact discs, RAM(random access memory) disks, CD-ROM discs, and DVD's. In addition touses directed to electronic components, the method of the presentinvention can be used to laminate other substrates that may be opaque tolight of wavelengths of 400 nm or less or to certain regions of visibleand near-IR light. These substrates may include those useful inmultilayer and tamper-evident documents such as passports, credit cards,smart cards, and the like. Substrates may also include multilayer ormetallized reflective films, such as those useful in optical systems. Inaddition, the method of the invention can be used for lamination orcuring of structural materials such as fiberglass-reinforced polymersthat may be useful in the manufacture of sporting goods such as boats,aircraft, or other vehicles. The method of the invention can be used toattach, for example, automobile rearview mirror assemblies toUV-absorbing windshields by irradiation through the windshield.

Substrates that are useful in the present invention include varioustransparent, translucent, or opaque materials such as plastics,ceramics, glasses, films, and papers. Reflective substrates useful inthe invention include metallized films, multilayer optical films such asthose described in U.S. Pat. Nos. 5,759,467, 5,822,774, 5,540,878,5,448,404, 5,380,479, 5,234,729, 5,217,794, 5, 202,074, and 5,122,905,incorporated herein by reference, and retroreflective films such asthose described in U.S. Pat. No. 4,025,159, incorporated herein byreference. Colored and opaque substrates including alumina, polyimide,and printed circuit substrates such as, for example, FR4, FR0406, and BTepoxy, including those having a colored solder mask or a coloredcoating, can be used, provided they are sufficiently light transmissiveto allow initiation of the photopolymerization reactions describedherein. UV or light absorbing or reflecting substrates that aretransmissive to actinic radiation of wavelengths greater than 400 to1200 nm can make useful substrates for the present invention. There isno particular limit to the thickness of the substrates useful in thepresent invention so long as sufficient visible or near IR light can betransmitted therethrough to effect the polymerization reactionsdescribed herein.

The present invention provides curing on a variety of substratespreviously not possible by conventional UV cure using visible-light andnear IR-curable adhesive systems. These include adhesion of reflectivefilms to colored plastic substrates, metal sputtered films to epoxysubstrates, articles to temperature sensitive substrates, and,generally, adhesion of translucent, opaque or reflective substrates toeach other in any combination thereof. In addition, irradiation asdescribed herein can be accomplished through either or both sides of thesubstrates. Further, irradiation as described herein can be direct or itcan be reflected from a mirrored surface.

The photocurable compositions of the present invention can be liquids,gels, or films. Photopolymerizable compositions useful in the inventionmay include free-radically polymerizable, cationically-polymerizable andhydrosilation-polymerizable moieties. Such compositions comprise aphotopolymerizable moiety and a visible- and/or near infrared-lightphotoinitiator therefor.

In one embodiment, the present invention provides a photopolymerizablecomposition comprising at least one cationically-polymerizable materialand a photoinitiation system active in the spectral region of greaterthan 400 to 1200 nm. Examples of organic materials polymerizable bycationic polymerization and suitable for the hardenable compositionsaccording to the invention are of the following types, it being possiblefor these to be used by themselves or as mixtures of at least twocomponents:

A. Ethylenically unsaturated compounds polymerizable by a cationicmechanism. These include:

1. Monoolefins and diolefins, for example isobutylene, butadiene,isoprene, styrene, α-methylstyrene, divinylbenzenes, N-vinylpyrrolidone,N-vinylcarbazole and acrolein.

2. Vinyl ethers, for example methyl vinyl ether, isobutyl vinyl ether,trimethylopropane trivinyl ether and ethylene glycol divinyl ether; andcyclic vinyl ethers, for example 3,4-dihydro-2-formyl-2H-pyran (acroleindimer) and the 3,4-dihydro-2H-pyran-2-carboxylic acid ester of2-hydroxymethyl-3,4-dihydro-2H-pyran.

3. Vinyl esters, for example vinyl acetate and vinyl stearate.

B. Heterocyclic compounds polymerizable by cationic polymerization, forexample ethylene oxide, propylene oxide, epichlorohydrin, glycidylethers of monohydric alcohols or phenols, for example n-butyl glycidylether, n-octyl glycidyl ether, phenyl glycidyl ether and cresyl glycidylether; glycidyl acrylate, glycidyl methacrylate, styrene oxide andcyclohexene oxide; oxetanes such as 3,3-dimethyloxetane and3,3-di(chloromethyl)oxetane; tetrahydrofuran; dioxolanes, trioxane and1,3,6-trioxacyclooctane; spiroorthocarbonates; lactones such asβ-propiolactone, γ-valerolactone and ε-caprolactone; thiiranes such asethylene sulfide and propylene sulfide; azetidines such asN-acylazetidines, for example N-benzoylazetidine, as well as the adductsof azetidine with diisocyanates, for example toluene-2,4-diisocyanateand toluene-2,6-diisocyanate and 4,4′-diaminodiphenylmethanediisocyanate; epoxy resins; and linear and branched polymers withglycidyl groups in the side-chains, for example homopolymers andcopolymers of polyacrylate and polymethacrylate glycidyl esters.

Of particular importance among these above-mentioned polymerizablecompounds are the epoxy resins and especially the diepoxides andpolyepoxides and epoxy resin prepolymers of the type used to preparecrosslinked epoxy resins.

Epoxy compounds that can be cured or polymerized by the processes ofthis invention are those known to undergo cationic polymerization andinclude 1,2-, 1,3-, and 1,4-cyclic ethers (also designated as 1,2-,1,3-, and 1,4-epoxides). The “Encyclopedia of Polymer Science andTechnology”, 6, (1986), p. 322, provides a description of suitable epoxyresins. In particular, cyclic ethers that are useful include thecycloaliphatic epoxies such as cyclohexene oxide and the ERL™ seriestype of resins available from Union Carbide, New York, N.Y., such asvinylcyclohexene oxide, vinylcyclohexene dioxide (ERL™-4206),3,4-epoxy-6-methylcyclohexylmethyl-3,4-epoxy-6-methyl-cyclollexenecarboxylate (ERL™-4201), bis(2,3-epoxycyclopentyl) ether (ERL™-0400),3,4-epoxycyclohexylmethyl-3,4-epoxycyclohexane carboxylate (ERL™-4221),bis-(3,4-epoxycyclohexyl) adipate (ERL™-4289), aliphatic epoxy modifiedfrom polypropylene glycol (ERL™-4050 and ERL™-4052), dipentene dioxide(ERL™-4269), and 2-(3,4-epoxycylclohexyl-5,5-spiro-3,4-epoxy)cyclohexene-meta-dioxane (ERL™-4234); also included are the glycidylether type epoxy resins such as propylene oxide, epichlorohydrin,styrene oxide, glycidol, the EPON™ series type of epoxy resins availablefrom Shell Chemical Co., Houston, Tex., including the diglycidyl eitherof bisphenol A and chain extended versions of this material such as EPON828™, EPON 1001™, EPON 1004™, EPON 1007™, EPON 1009™ and EPON 2002™ ortheir equivalent from other manufacturers; dicyclopentadiene dioxide;epoxidized vegetable oils such as epoxidized linseed and soybean oilsavailable as VIKOLOX™ and VIKOFLEX™ resins from Elf Atochem NorthAmerica, Inc., Philadelphia, Pa.; epoxidized KRATON™ LIQUID Polymers,such as L-207 available from Shell Chemical Co., Houston, Tex.;epoxidized polybutadienes such as the POLY BD™ resins from Elf Atochem,Philadelphia, Pa.; 1,4-butanediol diglycidyl ether, polyglycidyl etherof phenolformaldehyde; epoxidized phenolic novolac resins such as DEN431™ and DEN 438™ available from Dow Chemical Co., Midland Mich.;epoxidized cresol novolac resins such as ARALDITE™ ECN 1299 availablefrom Ciba, Hawthorn, N.Y.; resorcinol diglycidyl ether; epoxidizedpolystyrene/polybutadiene blends such as the EPOFRIEND™ resins such asEPOFRIEND A1010™ available from Daicel USA Inc., Fort Lee, N.J.; theHELOXY™ series of alkyl glycidyl ethers from Shell Chemical Co.,Houston, Tex., such as alkyl C₈-C₁₀ glycidyl ether (HELOXY Modifier 7™),alkyl C₁₂-C₁₄ glycidyl ether (HELOXY Modifier 8™), butyl glycidyl ether(HELOXY Modifier 61™), cresyl glycidyl ether (HELOXY Modifier 62™),p-tert-butylphenyl glycidyl ether (HELOXY Modifier 65™), polyfunctionalglycidyl ethers such as diglycidyl ether of 1,4-butanediol (HELOXYModifier 67™), diglycidyl ether of neopentyl glycol (HELOXY Modifier68™), diglycidyl ether of cyclohexanedimethanol (HELOXY Modifier 107™),trimethylol ethane triglycidyl ether (HELOXY Modifier 44), trimethylolpropane triglycidyl ether (HELOXY Modifier 48™), polyglycidyl ether ofan aliphatic polyol (HELOXY Modifier 84™), polyglycol diepoxide (HELOXYModifier 32™); and bisphenol F epoxides.

The preferred epoxy resins include the ERL type of resins especially3,4-epoxycyclohexylmethyl-3,4-epoxycyclohexanecarboxylate,bis-(3,4-epoxycyclohexyl) adipate and2-(3,4-epoxycylclohexyl-5,5-spiro-3,4-epoxy) cyclohexene-meta-dioxaneand the bisphenol A EPON type resins including2,2-bis-(p-(2,3-epoxypropoxy)phenylpropane) and chain extended versionsof this material. It is also within the scope of this invention to use ablend of more than one epoxy resin.

It is also within the scope of this invention to use one or more epoxyresins blended together. The different kinds of resins can be present inany proportion.

Optionally, monohydroxy- and polyhydroxy-alcohols may be added to thecurable compositions of the invention, as chain-extenders for the epoxyresin. The hydroxyl-containing material used in the present inventioncan be any organic material having hydroxyl functionality of at least 1,and preferably at least 2.

Preferably the hydroxyl-containing material contains two or more primaryor secondary aliphatic hydroxyl groups (i.e., the hydroxyl group isbonded directly to a non-aromatic carbon atom). The hydroxyl groups canbe terminally situated, or they can be pendent from a polymer orcopolymer. The molecular weight of the hydroxyl-containing organicmaterial can vary from very low (e.g., 32) to very high (e.g., onemillion or more). Suitable hydroxyl-containing materials can have lowmolecular weights, i.e., from about 32 to 200, intermediate molecularweight, i.e., from about 200 to 10,000, or high molecular weight, i.e.,above about 10,000. As used herein, all molecular weights are weightaverage molecular weights.

The hydroxyl-containing material can optionally contain otherfunctionalities that do not substantially interfere with cationic cureat room temperature. Thus, the hydroxyl-containing materials can benonaromatic in nature or can contain aromatic functionality. Thehydroxyl-containing material can optionally contain heteroatoms in thebackbone of the molecule, such as nitrogen, oxygen, sulfur, and thelike, provided that the ultimate hydroxyl-containing material does notsubstantially interfere with cationic cure at room temperature. Thehydroxyl-containing material can, for example, be selected fromnaturally occurring or synthetically prepared cellulosic materials. Ofcourse, the hydroxyl-containing material is also substantially free ofgroups which may be thermally or photolytically unstable; that is, thematerial will not decompose or liberate volatile components attemperatures below about 100° C. or in the presence of actinic lightwhich may be encountered during the desired curing conditions for thephotocopolymerizable composition.

Useful hydroxyl-containing materials are described, for example, in U.S.Pat. No. 5,856,373, which is incorporated herein by reference.

The amount of hydroxyl-containing organic material used in thecompositions of the invention may vary over broad ranges, depending uponfactors such as the compatibility of the hydroxyl-containing materialwith the epoxide, the equivalent weight and functionality of thehydroxyl-containing material, the physical properties desired in thefinal cured composition, the desired speed of photocure, and the like.

Blends of various hydroxyl-containing materials may be useful inadhesives of the invention. Examples of such blends include two or moremolecular weight distributions of hydroxyl-containing compounds, such aslow molecular weight (below 200), intermediate molecular weight (about200 to 10,000) and higher molecular weight (above about 10,000).Alternatively or additionally, the hydroxyl-containing material cancontain a blend of hydroxyl-containing materials having differentchemical natures, such as aliphatic and aromatic, or functionalities,such as polar and non-polar. As an additional example, one may usemixtures of two or more poly-functional hydroxy materials or one or moremono-functional hydroxy materials with poly-functional hydroxymaterials.

Any cationically-reactive vinyl ether may be used in the polymerizablecompositions of the present invention. Examples of vinyl ethers that maybe used include tri(ethyleneglycol) divinyl ether (RAPI-CURE™ DVE-3,available from International Specialty Products, Wayne, N.J.),di(ethyleneglycol) divinyl ether, di(ethyleneglycol) monovinyl ether,ethylene glycol monovinyl ether, triethyleneglycol methyl vinyl ether,tetraethyleneglycol divinyl ether, glycidyl vinyl ether, butanediolvinyl ether, butanediol divinyl ether, 1,4-cyclohexanedimethanol divinylether (RAPI-CURE CHVE, International Specialty Products),1,4-cyclohexanedimethanol monovinyl ether,4-(1-propenyloxymethyl)-1,3-dioxolan-2-one, 2-chloroethyl vinyl ether,2-ethylhexyl vinyl ether, methyl vinyl ether, ethyl vinyl ether,n-propyl vinyl ether, isopropyl vinyl ether, n-, iso- and t-butyl vinylethers, octadecyl vinyl ether, cyclohexyl vinyl ether, 4-hydroxybutylvinyl ether, t-amyl vinyl ether, dodecyl vinyl ether, hexanediol di- andmono-vinyl ethers, trimetylolpropane trivinyl ether (TMPTVE, availablefrom BASF Corp., Mount Olive, N.J.), aminopropyl vinyl ether,poly(tetrahydrofuran) divinyl ether, PLURIOL™ E200 divinyl ether,ethylene glycol butyl vinyl ether, 2-diethylaminoethyl vinyl ether,dipropylene glycol divinyl ether, and the VECTOMER™ divinyl ether resinscommercially available from Allied Signal Inc., Morristown, N.J., suchas a vinyl ether terminated aromatic urethane oligomer (VECTOMER™ 2010and VECTOMER™ 2015), a vinyl ether terminated aliphatic urethaneoligomer (VECTOMER™ 2020), hydroxybutyl vinyl ether isophthalate(VECTOMER™ 4010), and cyclohexane dimethanol monovinyl ether glutarate(VECTOMER™ 4020), or their equivalent from other manufacturers. It iswithin the scope of this invention to use a blend of more than one vinylether resin.

It is also within the scope of this invention to use one or more epoxyresins blended with one or more vinyl ether resins. The different kindsof resins can be present in any proportion.

Bifunctional monomers may also be used and examples that are useful inthis invention possess at least one cationically polymerizablefunctionality or a functionality that copolymerizes with cationicallypolymerizable monomers, e.g., functionalities that will allow anepoxy-alcohol copolymerization.

When two or more polymerizable compositions are present, they can bepresent in any proportion.

The broad class of cationic photoactive groups recognized in thecatalyst and photoinitiator industries may be used in the practice ofthe present invention. Photoactive cationic nuclei, photoactive cationicmoieties, and photoactive cationic organic compounds are art recognizedclasses of materials as exemplified by U.S. Pat. Nos. 4,250,311;3,708,296; 4,069,055; 4,216,288; 5,084,586; 5,124,417; 4,985,340,5,089,536, and 5,856,373, each of which is incorporated herein byreference.

The cationically-curable materials can be combined with a threecomponent or ternary photoinitiator system. Three component initiatorsystems are described in U.S. Pat. No. 5,545,676, U.S. application Ser.Nos. 08/838,835, and 08/840,093, both of which are now allowed, each ofwhich is incorporated herein by reference. The first component in thephotoinitiator system can be an iodonium salt, i.e., a diaryliodoniumsalt. The iodonium salt desirably is soluble in the monomer andpreferably is shelf-stable, meaning it does not spontaneously promotepolymerization when dissolved therein in the presence of the sensitizerand donor. Accordingly, selection of a particular iodonium salt maydepend to some extent upon the particular monomer, sensitizer and donorchosen. Suitable iodonium salts are described in U.S. Pat. Nos.3,729,313, 3,741,769, 3,808,006, 4,250,053 and 4,394,403, the iodoniumsalt disclosures of which are incorporated herein by reference. Theiodonium salt can be a simple salt, containing an anion such as Cl⁻,Br⁻, I⁻ or C₄H₅SO₃ ⁻; or a metal complex salt containing an antimonate,arsenate, phosphate or borate such as SbF₅OH⁻ or AsF₆ ⁻. Mixtures ofiodonium salts can be used if desired.

Examples of useful aromatic iodonium complex salt photoinitiatorsinclude: diphenyliodonium tetrafluoroborate; di(4-methylphenyl)iodoniumtetrafluoroborate; phenyl-4-methylphenyliodonium tetrafluoroborate;di(4-heptylphenyl)iodonium tetrafluoroborate; di(3-nitrophenyl)iodoniumhexafluorophosphate; di(4-chlorophenyl)iodonium hexafluorophosphate;di(naphthyl)iodonium tetrafluoroborate;di(4-trifluoromethylphenyl)iodonium tetrafluoroborate; diphenyliodoniumhexafluorophosphate; di(4-methylphenyl)iodonium hexafluorophosphate;diphenyliodonium hexafluoroarsenate; di(4-phenoxyphenyl)iodoniumtetrafluoroborate; phenyl-2-thienyliodonium hexafluorophosphate;3,5-dimethylpyrazolyl-4-phenyliodonium hexafluorophosphate;diphenyliodonium hexafluoroantimonate; 2,2′-diphenyliodoniumtetrafluoroborate; di(2,4-dichlorophenyl)iodonium hexafluorophosphate;di(4-bromophenyl)iodonium hexafluorophosphate;di(4-methoxyphenyl)iodonium hexafluorophosphate;di(3-carboxyphenyl)iodonium hexafluorophosphate;di(3-methoxycarbonylphenyl)iodonium hexafluorophosphate;di(3-methoxysulfonylphenyl)iodonium hexafluorophosphate;di(4-acetamidophenyl)iodonium hexafluorophosphate;di(2-benzothienyl)iodonium hexafluorophosphate; and diphenyliodoniumhexafluoroantimonate (DPISbF₆).

Of the aromatic iodonium complex salts which are suitable for use in thecompositions of the invention diaryliodonium hexafluorophosphate anddiaryliodonium hexafluoroantimonate are among the preferred salts. Thesesalts are preferred because, in general, they promote faster reaction,and are more soluble in inert organic solvents than are other aromaticiodonium salts of complex ions.

The second component in the photoinitiator system is the sensitizer. Thesensitizer desirably is soluble in the monomer, and is capable of lightabsorption somewhere within the range of wavelengths of greater than 400to 1200 nanometers, and is chosen so as not to interfere with thecationic curing process.

Suitable sensitizers desirably include compounds in the followingcategories: ketones, coumarin dyes (e.g., ketocoumarins), xanthene dyes,acridine dyes, thiazole dyes, thiazine dyes, oxazine dyes, azine dyes,aminoketone dyes, porphyrins, aromatic polycyclic hydrocarbons,p-substituted aminostyryl ketone compounds, aminotriaryl methanes,merocyanines, squarylium dyes and pyridinium dyes. Ketones (e.g.,monoketones or alpha-diketones), ketocoumarins, aminoarylketones andp-substituted aminostyryl ketone compounds are preferred sensitizers.For applications requiring high sensitivity (e.g., graphic arts), it ispreferred to employ a sensitizer containing a julolidinyl moiety. Forapplications requiring deep cure (e.g., cure of highly-filledcomposites), it is preferred to employ sensitizers having an extinctioncoefficient below about 1000, more preferably below about 100, at thedesired wavelength of irradiation for photopolymerization.Alternatively, dyes that exhibit reduction in light absorption at theexcitation wavelength upon irradiation can be used.

By way of example, a preferred class of ketone sensitizers has theformula:

ACO(X)_(b)B

where X is CO or CR⁵ R⁶, where R⁵ and R⁶ can be the same or different,and can be hydrogen, alkyl, alkaryl or aralkyl, b is zero or one, and Aand B can be the same or different and can be substituted (having one ormore non-interfering substituents) or unsubstituted aryl, alkyl,alkaryl, or aralkyl groups, or together A and B can form a cyclicstructure which can be a substituted or unsubstituted cycloaliphatic,aromatic, heteroaromatic or fused aromatic ring.

Suitable ketones of the above formula include monoketones (b=0) such as2,2-, 4,4- or 2,4-dihydroxybenzophenone, di-2-pyridyl ketone,di-2-furanyl ketone, di-2-thiophenyl ketone, benzoin, fluorenone,chalcone, Michler's ketone, 2-fluoro-9-fluorenone, 2-chlorothioxanthone,acetophenone, benzophenone 1- or 2-acetonaphthone, 9-acetylanthracene,2-, 3- or 9-acetylphenanthrene, 4-acetylbiphenyl, propiophenone,n-butyrophenone, valerophenone, 2-, 3- or 4-acetylpyridine,3-acetylcoumarin and the like. Suitable diketones includearalkyldiketones such as anthraquinone, phenanthrenequinone, o-, m- andp-diacetylbenzene, 1,3-, 1,4-, 1,5-, 1,6-, 1,7- and1,8-diacetylnaphthalene, 1,5-, 1,8- and 9,10-diacetylanthracene, and thelike. Suitable alpha-diketones (b=1 and X=CO) include 2,3-butanedione,2,3-pentanedione, 2,3-hexanedione, 3,4-hexanedione, 2,3-heptanedione,3,4-heptanedione, 2,3-octanedione, 4,5-octanedione, benzil, 2,2′-3,3′-and 4,4′-dihydroxylbenzil, furil, di-3,3′-indolylethanedione,2,3-bornanedione (camphorquinone), biacetyl, 1,2-cyclohexanedione,1,2-naphthaquinone, acenaphthaquinone, and the like.

The third component of the initiator system is an electron donor. Theelectron donor compound(s) desirably meets the requirements set forth inU.S. application Ser. Nos. 08/838,835, and 08/840,093, both of which arenow allowed, each of which is incorporated herein by reference, and aresoluble in the polymerizable composition. The donor can also be selectedin consideration of other factors, such as shelf stability and thenature of the polymerizable materials, iodonium salt and sensitizerchosen. A class of donor compounds that may be useful in the inventivesystems may be selected from some of the donors described in U.S. Pat.No. 5,545,676. Possible donor compounds that meet the criteria set forththerein must then be tested using one or both of the methods set forthbelow to determine if they will be useful donors for thephotopolymerizable compositions of the invention.

The donor is typically an alkyl aromatic polyether or an N-alkylarylamino compound wherein the aryl group is substituted by one or moreelectron withdrawing groups. Examples of suitable electron withdrawinggroups include carboxylic acid, carboxylic acid ester, ketone, aldehyde,sulfonic acid, sulfonate and nitrile groups.

A preferred group of N-alkyl arylamino donor compounds is described bythe following structural formula:

wherein each R¹ is independently H, C₁₋₁₈ alkyl that is optionallysubstituted by one or more halogen, —CN, —OH, —SH, C₁₋₁₈ alkoxy, C₁₋₁₈alkylthio, C₃₋₁₈ cycloalkyl, aryl, COOH, COOC₁₋₁₈ alkyl, (C₁₋₁₈alkyl)₀₋₁—CO—C₁₋₈ alkyl, SO₃R², CN or an aryl group that is optionallysubstituted by one or more electron withdrawing groups, or the R¹ groupsmay be joined to form a ring; and Ar is aryl that is substituted by oneor more electron withdrawing groups. Suitable electron withdrawinggroups include —COOH, —COOR², —SO₃R², —CN, —CO—C₁₋₁₈ alkyl and —C(O)Hgroups, wherein R² can be a C₁₋₁₈ straight-chain, branched, or cyclicalkyl group.

A preferred group of aryl alkyl polyethers has the following structuralformula:

wherein n=1-3 each R³ is independently H or C₁₋₁₈ alkyl that isoptionally substituted by one or more halogen, —CN, —OH, —SH, C₁₋₁₈alkoxy, C₁₋₁₈ alkylthio, C₃₋₁₈ cycloalkyl, aryl, substituted aryl,—COOH, —COOC₁₋₈ alkyl, —(C₁₋₁₈ alkyl)₀₋₁—COH, —(C₁₋₁₈ alkyl)₀₋₁—CO—C₁₋₁₈alkyl, —CO—C₁₋₁₈ alkyl, —C(O)H or —C₂₋₁₈ alkenyl groups and each R⁴ canbe C₁₋₁₈ alkyl that is optionally substituted by one or more halogen,—CN, —OH, —SH, C₁₋₁₈ alkoxy, C₁₋₁₈ alkylthio, C₃₋₁₈ cycloalkyl, aryl,substituted aryl, —COOH, —COOC₁₋₁₈ alkyl, —(C₁₋₁₈ alkyl)₀₋₁—COH, —(C₁₋₁₈alkyl)₀₋₁—CO—C₁₋₁₈ alkyl, —CO—C₁₋₁₈ alkyl, —C(O)H or —C₂₋₁₈ alkenylgroups.

In each of the above formulas the alkyl groups can be straight-chain orbranched, and the cycloalkyl group preferably has 3 to 6 ring carbonatoms but may have additional alkyl substitution up to the specifiednumber of carbon atoms. The aryl groups may be carbocyclic orheterocyclic aryl, but are preferably carbocyclic and more preferablyphenyl rings.

Preferred donor compounds include 4-dimethylaminobenzoic acid, ethyl4-dimethylaminobenzoate, 3-dimethylaminobenzoic acid,4-dimethylaminobenzoin, 4-dimethylaminobenzaldehyde,4-dimethylaminobenzonitrile and 1,2,4-trimethoxybenzene.

The photoinitiator compounds are provided in an amount effective toinitiate or enhance the rate of cure of the resin system. It has beenfound that the amount of donor that is used can be critical particularlywhen the donor is an amine. Too much donor can be deleterious to cureproperties. Preferably, the sensitizer is present in about 0.05-5 weightpercent based on resin compounds of the overall composition. Morepreferably, the sensitizer is present at 0.10-1.0 weight percent.Similarly, the iodonium initiator is preferably present at 0.05-10.0weight percent, more preferably at 0.10-5.0 weight percent, and mostpreferably 0.50-3.0 weight percent. Likewise, the donor is preferablypresent at 0.01-5.0 weight percent, more preferably 0.05-1.0 weightpercent, and most preferably 0.05-0.50 weight percent.

Photopolymerizable compositions useful in the invention are prepared bysimply admixing, under “safe light” conditions, the components asdescribed above. Suitable inert solvents may be employed if desired wheneffecting this mixture. Any solvent may be used which does not reactappreciably with the components of the inventive compositions. Examplesof suitable solvents include acetone, dichloromethane, and acetonitrile.A liquid material to be polymerized may be used as a solvent for anotherliquid or solid material to be polymerized. Solventless compositions canbe prepared by simply dissolving an aromatic iodonium complex salt andsensitizer in an epoxy resin-polyol mixture with or without the use ofmild heating to facilitate dissolution.

An alternative photoinitiator system for cationic polymerizationsincludes the use of organometallic complex cations essentially free ofmetal hydride or metal alkyl functionality selected from those describedin U.S. Pat. No. 4,985,340, and such description is incorporated hereinby reference and has the formula:

[(L¹)(L²)M]^(+q)  (1)

wherein

M represents a metal selected from the group consisting of Cr, Mo, W,Mn, Re, Fe, Ru, Os, Co, Rh, Ir, Pd, Pt and Ni, preferably Cr, Mo, W, Mn,Fe, Ru, Co, Pd, and Ni; and most preferably Mn and Fe;

L¹ represents 1 or 2 cyclic, polyunsaturated ligands that can be thesame or different ligand selected from the group consisting ofsubstituted and unsubstituted cyclopentadienyl, cyclohexadienyl, andcycloheptatrienyl, cycloheptatriene, cyclooctatetraene, heterocycliccompounds and aromatic compounds selected from substituted orunsubstituted arene compounds and compounds having 2 to 4 fused rings,and units of polymers, e.g., a phenyl group of polystyrene,poly(styrene-co-butadiene), poly(styrene-co-methyl methacrylate),poly(a-methylstyrene), and the like; a cyclopentadiene group ofpoly(vinylcyclopentadiene); a pyridine group of poly(vinylpyridine), andthe like, each capable of contributing 3 to 8 electrons to the valenceshell of M;

L² represents none, or 1 to 3 nonanionic ligands contributing an evennumber of electrons that can be the same or different ligand selectedfrom the group of carbon monoxide, ketones, olefins, ethers,nitrosonium, phosphines, phosphites, and related derivatives of arsenicand antimony, organonitriles, amines, alkynes, isonitriles, dinitrogen,with the proviso that the total electronic charge contributed to Mresults in a net residual positive charge of q to the complex;

q is an integer having a value of 1 or 2, the residual charge of thecomplex cation.

Organometallic salts are known in the art and can be prepared asdescribed in, for example, EPO No. 094,914 and U.S. Pat. Nos. 5,089,536,4,868,288, and 5,073,476, and such descriptions are incorporated hereinby reference.

Examples of preferred cations include:

diphenyliodonium, ditolyliodonium, didodecylphenyliodonium,(4-octyloxyphenyl)phenyliodonium, and bis(methoxyphenyl)iodonium;

triphenylsulfonium, diphenyl-4-thiophenoxyphenylsulfonium, and1,4-phenylene-bis(diphenylsufonium);

bis(η⁵-cyclopentadienyl)iron(1+), bis(η⁵-methylcyclopentadienyl)iron(1+),

(η⁵-cyclopentadienyl)(η⁵-methylcyclopentadienyl)iron (1+), andbis(η⁵-trimethylsilylcyclopentadienyl)iron (1+);

bis(η⁶-xylenes)iron (2+), bis(η⁶-mesitylene)iron (2+),bis(η⁶-durene)iron (2+), bis(η⁶-pentamethylbenzene)iron (2+), andbis(η⁶-dodecylbenzene) iron (2+);

(η⁵-cyclopentadienyl)(η⁶-xylenes)iron(1+) commonly abbreviated as(CpFeXy)(1+),

(η⁵-cyclopentadienyl)(η⁶-toluene)iron(1+),

(η⁵-cyclopentadienyl)(η⁶-mesitylene)iron(1+),

(η⁵-cyclopentadienyl)(η⁶-pyrene)iron(1+),

(η⁵-cyclopentadienyl)(η⁶-naphthalene)iron(1+), and

(η⁵-cyclopentadienyl)(η⁶-dodecylphenyl)iron(1+).

In another embodiment, the present invention provides aphotopolymerizable composition comprising at least one freeradically-polymerizable material and a photoinitiation system active inthe spectral region of greater than 400 to 1200 nm.

Suitable free radically-polymerizable monomers may contain at least oneethylenically-unsaturated double bond, can be oligomers or polymers, andare capable of undergoing addition polymerization. Such monomers includemono-, di- or poly-acrylates and methacrylates such as methyl acrylate,methyl methacrylate, ethyl acrylate, isopropyl methacrylate, n-hexylacrylate, stearyl acrylate, allyl acrylate, glycerol diacrylate,glycerol triacrylate, ethyleneglycol diacrylate, diethyleneglycoldiacrylate, triethyleneglycol dimethacrylate, 1,3-propanedioldiacrylate, 1,3-propanediol dimethacrylate, trimethylolpropanetriacrylate, 1,2,4-butanetriol trimethacrylate, 1,4-cyclohexanedioldiacrylate, pentaerythritol triacrylate, pentaerythritol tetraacrylate,pentaerythritol tetramethacrylate, sorbitol hexacrylate,bis[1-(2-acryloxy)]-p-ethoxyphenyldimethylmethane,bis[1-(3-acryloxy-2-hydroxy)]-p-propoxyphenyldimethylmethane,tris(hydroxyethylisocyanurate) trimethacrylate; the bis-acrylates andbis-methacrylates of polyethylene glycols of molecular weight 200-500,copolymerizable mixtures of acrylated monomers such as those of U.S.Pat. No. 4,652,274, incorporated herein by reference, and acrylatedoligomers such as those of U.S. Pat. No. 4,642,126, incorporated hereinby reference; unsaturated amides such as methylene bis-acrylamide,methylene bis-methacrylamide, 1,6-hexamethylene bis-acrylamide,diethylene triamine tris-acrylamide and beta-methacrylaminoethylmethacrylate; and vinyl compounds such as styrene, diallyl phthalate,divinyl succinate, divinyl adipate and divinylphthalate. Mixtures of twoor more monomers can be used if desired.

A variety of visible or near-IR photoinitiator systems may be used forphotopolymerization of free-radically polymerizable materials useful inthe invention. For example, the monomer can be combined with a threecomponent or ternary photoinitiator system. The first component in thephotoinitiator system is the iodonium salt, i.e., a diaryliodonium salt.The iodonium salt desirably is soluble in the monomer and preferably isshelf-stable (i.e., does not spontaneously promote polymerization) whendissolved therein in the presence of the sensitizer and donor.Accordingly, selection of a particular iodonium salt may depend to someextent upon the particular monomer, polymer or oligomer, sensitizer anddonor chosen. Suitable iodonium salts are described in U.S. Pat. Nos.3,729,313, 3,741,769, 3,808,006, 4,250,053 and 4,394,403, the iodoniumsalt disclosures of which are incorporated herein by reference. Theiodonium salt can be a simple salt (e.g., containing an anion such asCl⁻, Br⁻, I⁻ or C₄ H₅ SO₃ ⁻) or a metal complex salt (e.g., containingSbF₅OH⁻ or AsF₆ ⁻). Mixtures of iodonium salts can be used if desired.

Preferred iodonium salts include diphenyliodonium salts such asdiphenyliodonium chloride, diphenyliodonium hexafluorophosphate anddiphenyliodonium tetrafluoroborate.

The second component in the photoinitiator system is a sensitizer. Thesecompounds have been disclosed above as sensitizers useful forcationically-curable materials. The sensitizer desirably is soluble inthe monomer, and is capable of light absorption somewhere within therange of wavelengths of greater than 400 to 1200 nanometers, morepreferably greater than 400 to 700 nanometers and most preferablygreater than 400 to about 600 nanometers. The sensitizer may also becapable of sensitizing 2-methyl-4,6-bis(trichloromethyl)-s-triazine,using the test procedure described in U.S. Pat. No. 3,729,313, which isincorporated herein by reference. Preferably, in addition to passingthis test, a sensitizer is also selected based in part upon shelfstability considerations. Accordingly, selection of a particularsensitizer may depend to some extent upon the particular monomer,oligomer or polymer, iodonium salt and donor chosen.

Preferred donors, the third component of the photoinitiator system,include amines (including aminoaldehydes and aminosilanes), amides(including phosphoramides), ethers (including thioethers), ureas(including thioureas), ferrocene, sulfinic acids and their salts, saltsof ferrocyanide, ascorbic acid and its salts, dithiocarbamic acid andits salts, salts of xanthates, salts of ethylene diamine tetraaceticacid and salts of tetraphenylboronic acid. The donor can beunsubstituted or substituted with one or more non-interferingsubstituents. Particularly preferred donors contain an electron donoratom such as a nitrogen, oxygen, phosphorus, or sulfur atom, and anabstractable hydrogen atom bonded to a carbon or silicon atom alpha tothe electron donor atom. A wide variety of donors is disclosed in U.S.Pat. No. 5,545,676, which is incoporated herein by reference.

Free-radical initiators useful in the invention, e.g., those that arephotochemically active in the wavelength region of greater than 400 to1200 nm, also may include the class of acylphosphine oxides, asdescribed in European Patent Application No. 173567. Such acylphosphineoxides are of the general formula

(R⁹)₂—P(═O)—C(═O)R¹⁰

wherein each R⁹ individually can be a hydrocarbyl group such as alkyl,cycloalkyl, aryl, and aralkyl, any of which can be substituted with ahalo-, alkyl- or alkoxy-group, or the two R⁹ groups can be joined toform a ring along with the phosphorous atom, and wherein R¹⁰ is ahydrocarbyl group, an S-, O-, or N-containing five- or six-memberedheterocyclic group, or a —Z—C(═O)—P(═O)—(R⁹)₂ group, wherein Zrepresents a divalent hydrocarbyl group such as alkylene or phenylenehaving from 2 to 6 carbon atoms.

Preferred acylphosphine oxides useful in the invention are those inwhich the R⁹ and R¹⁰ groups are phenyl or lower alkyl- or loweralkoxy-substituted phenyl. By “lower alkyl” and “lower alkoxy” is meantsuch groups having from 1 to 4 carbon atoms. Most preferably, theacylphosphine oxide is bis(2,4,6-trimethylbenzoyl)phenyl phosphine oxide(IRGACURE™ 819, Ciba Specialty Chemicals, Tarrytown, N.Y.).

Tertiary amine reducing agents may be used in combination with anacylphosphine oxide. Illustrative tertiary amines useful in theinvention include ethyl 4-(N,N-dimethylamino)benzoate andN,N-dimethylaminoethyl methacrylate. The initiator can be employed incatalytically-effective amounts, such as from about 0.1 to about 5weight percent, based on the weight of ethylenically-unsaturatedcompound present, of the acylphosphine oxide plus from about 0.1 toabout 5 weight percent, based on the weight of ethylenically-unsaturatedcompound present, of the tertiary amine.

Commercially-available phosphine oxide photoinitiators capable offree-radical initiation when irradiated at wavelengths of greater than400 nm to 1200 nm include a 25:75 mixture, by weight, ofbis(2,6-dimethoxybenzoyl)-2,4,4-trimethylpentyl phosphine oxide and2-hydroxy-2-methyl-1-phenylpropan-1-one (IRGACURE™ 1700, Ciba SpecialtyChemicals),2-benzyl-2-(N,N-dimethylamino)-1-(4-morpholinophenyl)-1-butanone(IRGACURE™ 369, Ciba Specialty Chemicals),bis(η⁵-2,4-cyclopentadien-1-yl)-bis(2,6-difluoro-3-(1H-pyrrol-1-yl)phenyl)titanium (IRGACURE™ 784 DC, Ciba Specialty Chemicals), a 1:1 mixture, byweight, of bis(2,4,6-trimethylbenzoyl)phenyl phosphine oxide and2-hydroxy-2-methyl-1-phenylpropane-1-one (DAROCUR™ 4265, Ciba SpecialtyChemicals), and ethyl-2,4,6-trimethylbenzylphenyl phosphinate (LUCIRIN™LR8893X, BASF Corp., Charlotte, N.C.).

Free-radical initiators useful in the invention, e.g., those that arephotochemically active in the wavelength region of greater than 400 to1200 nm, also may include the class of ionic dye—counterion complexinitiators comprising a borate anion and a complementary cationic dye.Borate anions useful in these photointiators generally can be of theformula

R¹R²R³R⁴B⁻

wherein R¹, R², R³, and R⁴ independently can be alkyl, aryl, alkaryl,allyl, aralkyl, alkenyl, alkynyl, alicyclic and saturated or unsaturatedheterocyclic groups. Preferably, R², R³, and R⁴ are aryl groups and morepreferably phenyl groups, and R¹ is an alkyl group and more preferably asecondary alkyl group.

Cationic counterions can be cationic dyes, quaternary ammonium groups,transition metal coordination complexes, and the like. Cationic dyesuseful as counterions can be cationic methine, polymethine,triarylmethine, indoline, thiazine, xanthene, oxazine or acridine dyes.More specifically, the dyes may be cationic cyanine, carbocyanine,hemicyanine, rhodamine, and azomethine dyes. Specific examples of usefulcationic dyes include Methylene Blue, Safranine O, and Malachite Green.Quaternary ammonium groups useful as counterions can betrimethylcetylammonium, cetylpyridinium, and tetramethylammonium. Otherorganophilic cations can include pyridinium, phosphonium, and sulfonium.Photosensitive transition metal coordination complexes that may be usedinclude complexes of cobalt, ruthenium, osmium, zinc, iron, and iridiumwith ligands such as pyridine, 2,2′-bipyridine,4,4′-dimethyl-2,2′-bipyridine, 1,10-phenanthroline,3,4,7,8-tetramethylphenanthroline, 2,4,6-tri(2-pyridyl-s-triazine) andrelated ligands.

Borate salt photoinitiators are described, for example, in U.S. Pat.Nos. 4,772,530, 4,954,414, 4,874,450, 5,055,372, and 5,057,393, thedisclosures of which are incorporated herein by reference.

In a further embodiment, a third kind of photopolymerization reactionuseful in the invention includes the visible radiation-activatedaddition reaction of a compound containing silicon-bonded hydrogen witha compound containing aliphatic unsaturation. The addition reactiontypically can be referred to as hydrosilation. Hydrosilation by means ofvisible light has been described, e.g., in U.S. Pat. Nos. 4,916,169 and5,145,886, both of which are incorporated herein by reference

Reactants useful in the radiation-activated hydrosilation reactioninclude compounds containing aliphatic unsaturation or acetylenicunsaturation. These compounds are well known in the art of hydrosilationand are disclosed in such Patents as U.S. Pat. No. 3,159,662, U.S. Pat.No. 3,220,972, and U.S. Pat. No. 3,410,886, incorporated herein byreference. In instances where these unsaturated compounds containelements other than carbon and hydrogen, it is preferred that theseelements be either oxygen, nitrogen, silicon, a halogen, or acombination thereof. The aliphatically unsaturated compound can containone or more carbon-to-carbon multiple bonds. Representative examples ofthe aliphatically unsaturated hydrocarbons which can be employed includemono-olefins, for example, ethylene, propylene, and 2-pentene,diolefins, for example, divinylbenzene, butadiene, and 1,5-hexadiene,cycloolefins, for example, cyclohexene and cycloheptene, andmonoalkynes, for example, acetylene, propyne, and 1-butene-3-yne. Thealiphatically unsaturated compounds can have up to 20 to 30 carbonatoms, or more.

A particularly useful type of unsaturated compound, which can beemployed in the practice of the present invention, is that containingsilicon, such as those compounds commonly referred to as organosiliconmonomers or polymers. These unsaturated organosilicon compounds have atleast one aliphatically unsaturated organic group attached to siliconper molecule. Aliphatically unsaturated organosilicon compounds includesilanes, polysilanes, siloxanes, silazanes, as well as monomeric orpolymeric materials containing silicon atoms joined together bymethylene or polymethylene groups or by phenylene groups.

The reactant containing the silicon-hydrogen linkage can be a polymericcompound or a compound that is not polymeric. These compounds are wellknown in the art and are also disclosed in the patents which describethe aliphatically unsaturated reactant, as cited above. The reactantcontaining the silicon-hydrogen linkage should contain at least onesilicon-bonded hydrogen atom per molecule, with no more than threehydrogen atoms attached to any one silicon atom.

The hydrosilation composition useful in the synthesis of low molecularweight compounds by the process of the invention can be prepared bymixing about 0.1 to about 10.0 equivalent weights of the compound havingsilicon-bonded hydrogen with one equivalent weight of the compoundhaving aliphatic unsaturation and then adding an amount of platinumcomplex catalyst sufficient to catalyze the reaction. The amount of thecatalyst can range from about 5 to about 5000 parts by weight,preferably from about 25 to about 500 parts by weight, per 1,000,000parts by weight of the total composition.

Known techniques can be used to conduct the hydrosilation reaction. Incarrying out a hydrosilation reaction in the practice of this invention,the reactants and catalyst can be introduced into a vessel equipped forstirring, where the mixture is stirred and exposed to actinic radiationuntil the reaction is complete. If either of the reactants is a solid oris extremely viscous, a solvent can be introduced into the vessel tofacilitate uniform mixing of the reactants. Suitable solvents includearomatic hydrocarbons, such as xylene and toluene, aliphatichydrocarbons, such as hexane and mineral spirits, and halogenatedhydrocarbons, such as chlorobenzene and trichloroethane. It is desirablethat the solvent be transmissive to actinic radiation. From about 0.1 toabout 10 parts of solvent per part by weight of the combined reactantscan be used. The resulting reaction product will generally besufficiently pure for its intended use. However, it may be desirable toremove the solvent if one has been employed.

The thoroughly mixed composition can then be applied to a substrate as acontinuous or discontinuous layer by any suitable means, such asby-spraying, dipping, knife coating, curtain coating, roll coating, orthe like, and the coating cured by using conventional techniques forproviding actinic radiation. It is preferred that curing be conducted byexposing the coated substrate to radiation having a wavelength ofgreater than 400 nm to 1200 nm. Depending on the particular siliconeformulation, catalyst, and intensity of the actinic radiation, curingcan be accomplished in a period from less than one second to less than 2minutes.

Catalysts useful in hydrosilation reactions include certain platinumcomplexes, such as platinum complex catalysts having onecyclopentadienyl group that is eta-bonded to the platinum atom and threealiphatic groups that are sigma-bonded to the platinum atom, incombination with visible and near-IR light sensitizes, as disclosed inU.S. Pat. No. 4,916,169, and Pt(II) β-diketonates, as disclosed in U.S.Pat. No. 5,145,886, the disclosures of each of which are incorporatedherein by reference.

Representative examples of suitable (η⁵-cyclopentadienyl)trialiphaticplatinum complexes useful in the practice of this invention include thefollowing, in which (Cp) represents the (η⁵-cyclopentadienyl) group:(Cp)trimethylplatinum, (Cp)ethyldimethylplatinum, (Cp)triethylplatinum,(Cp)triallylplatinum, (Cp)tripentylplatinum, (Cp)trihexylplatinum,(methyl-Cp)trimethylplatinum, (trimethylsilyl-Cp)trimethylplatinum,(dimethylphenylsilyl-Cp)trimethylplatinum, and(Cp)acetyldimethylplatinum.

Other suitable (η⁵-cyclopentadienyl)trialiphaticplatinum complexessuitable for this invention are described in U.S. Pat. No. 4,510,094,incorporated herein by reference.

Sensitizers suitable for this embodiment of the invention are thosecompounds capable of absorbing actinic radiation within the visibleregion of the electromagnetic spectrum, i.e., greater than 400 nm toabout 800 nm, and capable of transferring energy to the platinumcomplex. In general, they must have a triplet energy level of at least31 Kcal/mole, and must not inhibit the hydrosilation reaction.Sensitizers are preferably selected from two classes of compounds: (1)polycyclic aromatic compounds and (2) aromatic compounds containing aketone chromophore. The sensitizer compounds can be substituted with anysubstituent that does not interfere with the light absorbing and energytransferring capabilities of the sensitizer compound or thehydrosilation catalyst. Examples of typical substituents include alkyl,alkoxy, aryl, aryloxy, aralkyl, alkaryl, halogen, etc. Representativeexamples of polycyclic aromatic sensitizers suitable for the inventioninclude anthracene, 9-vinylanthracene, 9,10-dimethylanthracene,9,10-dichloroanthracene, 9,10-dibromoanthracene, 9,10-diethylanthracene,9,10-diethoxyanthracene, 2-ethyl-9,10-dimethylanthracene, naphthacene,pentacene, benz(a)anthracene, 7,12-dimethylbenz(a)anthracene, azuleneand the like.

Representative examples of suitable Pt(II) beta-diketonate complexesinclude Pt(II) bis(2,4-pentanedionate), Pt(II) bis(2,4-hexanedionate),Pt(II) bis(2,4-heptanedionate), Pt(II) bis(3,5-heptanedionate), Pt(II)bis(1-phenyl-1,3-butanedionate), Pt(II)bis(1,3-diphenyl-1,3-propanedionate), and the like.

Compositions useful in the invention can contain a wide variety ofadjuvants depending upon the desired end use. Suitable adjuvants includesolvents, diluents, resins, binders, plasticizers, pigments, dyes,inorganic or organic reinforcing or extending fillers (at preferredamounts of about 10% to about 90% by weight, based on the total weightof the composition), thixotropic agents, indicators, inhibitors,stabilizers, UV absorbers, and the like. The amounts and types of suchadjuvants, and their manner of addition to a composition of theinvention will be familiar to those skilled in the art.

Actinic radiation of use in the present invention includes wavelengthswithin the range of greater than 400 to 1200 nm. Exemplary visible lightsources include, but are not limited to, the sun, lasers, metal vapor(sodium and mercury) lamps, incandescent lamps, halogen lamps, mercuryare lamps, fluorescent room light, flashlights, light emitting diodes,tungsten halogen lamps, and xenon flash lamps.

Methods of the present invention quickly and conveniently bond materialson demand indirectly through a variety of substrates utilizingphotopolymerizable compositions. The light curable compositions can bepre-applied as liquids or gels to the substrates. Alternatively,photocrosslinkable thermoplastic films can be pre-applied to either asubstrate or an article, and subsequently heated to provide a thermallyrepositionable adhesive that is permanently set upon light exposurethrough the substrate. This approach affords the ability to operate onboth temperature sensitive and insensitive substrates. Also, the presentinvention provides the ability to photopolymerize materials through UVor visible light absorbing substrates via judicious selection ofinitiator systems and light sources so as to find correspondence ofphotoinitiator absorbance and radiation source emission withtransmissive spectral regions of a substrate.

The key to successful photocuring of the photopolymerizable compositionsthrough, for example, circuit boards, recording disks, multilayerreflective films, and retroreflective films, is threefold: 1)identification of light transmissive spectral regions associated withthe various substrates; 2) identification of photoinitiators that absorblight at the transmission wavelengths of the substrates; and 3)selection of a light source that provides actinic radiation atwavelengths that are readily transmitted through the substrate andabsorbed by the photoinitiator.

Optical Density and Light Transmission

Optical density pertains to the light absorptivity (Abs) andcorresponding transmission (T) characteristics associated with aparticular material at a given thickness.

This concept is typically described by Beer's Law:

Abs=ebc where

e=molar absorptivity

b=thickness or path length of light absorbing material

c=concentration of light absorbing species

in addition,

Abs=−log T=or log 1/T

One can readily quantify light absorption (by utilizing UV/VISspectrometry) or transmission (by using an integrating sphere) andtherefore interconvert Abs and % T and subsequently predict lightabsorbing characteristics for a type or thickness of material:

For example:

Absorption (Optical density) % T 0.1 79.40 0.5 31.60 1.0 10.00 1.5 3.102.0 1.00 2.5 0.30 3.0 0.10 3.5 0.03 4.0 0.01 4.5 0.001

As the optical density or absorptivity increases the light transmissiondecreases. For example: the industry standard known as DVD 10, which isa two layer laminated polycarbonate disc coated with a metallic coatingon both sides and an adhesive sandwiched in between, typically has anoptical density between 2 and 3, equivalent to 0.1-0.3% lighttransmission through either side. The industry standard known as DVD 5is also a laminated construction, however, only one side is coated witha metallized film whereas the other half of the sandwich construction istypically a clear or transparent polycarbonate that readily transmitslonger wavelength UV and visible light. Materials with an opticaldensity greater than 1.5 can be challenging materials to photocurethrough without appropriate light sources, initiators and overallunderstanding of the desired substrates. Particularly challenging arereflective materials with optical densities of greater than 2 such asDVD 10. Characterization of absorption or transmission of varioussubstrates is essential to successful photocuring through the substrate.

Commonly used reflective materials in the prior art were perceived to benontransmissive to visible radiation. It is now appreciated that only aperfect mirror reflects 100% of incident radiation. The presentinvention provides a unique opportunity for photocuring through suchreflective substrates, which it is now appreciated can transmit light atcertain wavelengths in the visible or near IR range.

Articles that can be bonded to substrates using the method of thepresent invention include, for example, electronic components tosubstrates such as printed circuit boards or flexible printed circuits.Also useful are bonding steps such as board-to-board lamination,lamination of metal circuits or traces, assembly of connectors such asfiber optic connectors, or assembly of articles composed of metallizedsubstrates such as data storage disks including compact discs, RAM(random access memory) disks, CD-ROM discs, and DVD's. In addition touses directed to electronic components, the method of the presentinvention can be used to laminate other substrates that may be opaque tolight of wavelengths of 400 nm or less or to certain regions of visibleand near-IR light. These substrates may include those useful inmultilayer and tamper-evident documents such as passports, credit cards,smart cards, and the like. Substrates may also include multilayer ormetallized reflective films, such as those useful in optical systems. Inaddition, the method of the invention can be used for lamination orcuring of structural materials such as fiberglass-reinforced polymersthat may be useful in the manufacture of sporting goods such as boats,aircraft, or other vehicles. The method of the invention can be used toattach, for example, automobile rearview mirror assemblies toUV-absorbing windshields by irradiation through the windshield.

Objects and advantages of this invention are further illustrated by thefollowing examples. The particular materials and amounts thereof, aswell as other conditions and details, recited in the examples should notbe used to unduly limit this invention.

EXAMPLES

Unless otherwise specified, all materials were obtained, or areavailable, from Aldrich Chemical Co., Milwaukee, Wis.

Example 1

Two visible light polymerizable compositions were prepared as shown inTable 1, below:

TABLE 1 Adhesive Compositions 1A 1B Component (parts by weight) (partsby weight) Bis(phenol A) diglycidyl 50.00 50.00 dimethacrylate (Bis GMA)Triethyleneglycol 50.00 50.00 dimethacrylate (TEGDMA) Camphorquinone(CPQ) 00.17 00.10 Ethyl p- 01.00 01.00 dimethylaminobenzoate (EDMAB)Diphenyl iodonium 00.60 00.60 hexafluorophosphate (DPIPF₆) Rose Bengal(RB) 00.00 00.10

Composition 1A containing the sensitizer CPQ had a light absorbancebetween 400 and 500 nm whereas 1B containing both CPQ and RB absorbedbetween about 400 and 580 nm. One drop of 1A was applied to a region ofan FR4 epoxy printed circuit board (PCB) (available from TRC Circuits,Minneapolis, Minn.) free of conductive metal contacts on either side.The board was approximately 1.5 mm thick. The light guide of 3M XL3000dental curing light (with a light output between 400-500 nm, 3M, St.Paul, Minn.) was placed in direct contact with the PCB on the sidedirectly opposite the drop of adhesive. The light was activated forapproximately 10 seconds, whereupon the liquid polymerized to a hardsolid that was well adhered to the PCB. Composition 1B was evaluated ina similar manner and also was found to cure rapidly to a hard adhesivefilm. In addition, composition 1B, which was initially colored red,exhibited a visual change to near colorless upon light exposure andcuring.

In a second trial, compositions 1A and 1B were applied to two distinctregions of the PCB, the regions bearing copper metal traces. One regionhad traces of approximately evenly spaced lines per cm, and the otherhad traces of approximately 1 mm in width spaced 1.5 mm apart. A bead ofthe adhesive to be examined was applied across the traces so as to coverboth metallized and non-metallized surface. The various regions wereirradiated from the reverse side of the PCB for about 20 seconds, asdescribed for compositions 1A and 1B, above. Surprisingly, the liquidresins polymerized over all points of the PCB, including the metallizedtraces.

The above data show that a methacrylate functional composition readilyphotopolymerized through an FR4 epoxy printed circuit board at roomtemperature with visible light between 400-500 nm.

Example 2

A variety of UV and visible light photopolymerizable compositions wereprepared as illustrated below.

Stock Solution 1

A stock solution (Stock Solution 1) was prepared by combining 100 gramseach of Bis GMA and TEGDMA, followed by thorough mixing untilhomogeneous.

Ten photopolymerizable compositions were prepared by mixing 10.0 partsby weight of the stock solution with a photoinitiator or photoinitiatorsystem, as shown in Table 2A, below. Each composition contained adifferent photoinitiator capable of initiating free radicalpolymerization at a particular range of wavelengths.

TABLE 2A Adhesive Compositions Amount Parts by Example Photoinitiatorweight Wavelengths 2A (comparative) IRGACURE ™ 184¹ 00.30 (254-365 nm)2B (comparative) IRGACURE ™ 500² 00.30 (254-360 nm) 2C (comparative)IRGACURE ™ 651³ 00.30 (254-380 nm) 2D (comparative) IRGACURE ™ 907⁴00.30 (254-375 nm) 2E IRGACURE ™ 369⁵ 00.30 (254-425 nm) 2F IRGACURE ™1700⁶ 00.30 (254-425 nm) 2G CPQ 00.05 (400-500 nm) EDMAB 00.07 DPIPF₆00.06 2H Rose Bengal 00.015 (450-580 nm) EDMAB 00.07 DPIPF₆ 00.06 2IToluidine Blue O 00.01 (450-690 nm) EDMAB 00.05 DPIPF₆ 00.05 2JMethylene Blue 00.01 (500-700 nm) EDMAB 00.05 DPIPF₆ 00.50 ¹IRGACURE ™184 is 1-hydroxycyclohexyl phenyl ketone (HCPK), commercially availablefrom Ciba Specialty Chemicals Additives, Tarrytown, NY ²IRGACURE ™ 500is a mixture of 1-hydroxycyclohexyl phenyl ketone and benzophenone,commercially available from Ciba Specialty Chemicals Additives³IRGACURE ™ 651 is 2,2-dimethoxy-2-phenyl acetophenone (BDK),commercially available from Ciba Specialty Chemicals Additives⁴IRGACURE ™ 907 is 2-methyl-1-(4-methylthio)phenyl)-2-morpholinopropan-1-one (MMMP), commercially avaiable from Ciba Specialty ChemicalsAdditives ⁵IRGACURE ™ 369 is2-benzyl-2-N,N-dimethylamino-1-(4-morpholinophenyl)-1-butanone (DBMP),commercially avaiable from Ciba Specialty Chemicals Additives⁶IRGACURE ™ 1700 is a mixture comprising 25%bis(2,6-dimethoxybenzoyl)-2,4,4-trimethylpentyl phosphine oxide (DMBAPO)and 75% 2-hydroxy-2-methyl-1-phenyl-propan-1-one (HMPP), commerciallyavailable from Ciba Specialty Chemicals Additives

The above photopolymerizable compositions were evaluated forphotopolymerization gel times with three different light sources:1)EFOS™ Ultracure 100 medium pressure mercury are lamp (254, 313, 365,405, 430, 530, 545, 575, 590, 610 nm; EFOS, Inc., Mississauga, ON,Canada), 2) GE Light Engine™ (broad band visible 380-700 nm; GE LightingDiv. of GE Company, Cleveland, Ohio) and 3) 3M XL3000 dental curinglight (400-500 nm).

One drop of each of the above resins was transferred to a sheet ofpolyester film and irradiated with each of the three light sources froma distance of about 10 mm until a polymerized solid was obtained, up toa maximum of 60 seconds. The results of this trial established theability or inability of each composition to be photopolymerized witheach light source in the absence of the various printed circuit boardmaterials. The results can be found in Table 2C, below. Carefulselection of both the light source and photointiator system wasimportant for a successful polymerization to occur.

The above compositions were further examined for photopolymerizationthrough several different printed circuit board materials including: 1)alumina (white), 2) FR4 epoxy (yellow), 3) FR4 epoxy+green solder mask(green), 4) FR0406 epoxy (yellow), 5) BT-epoxy (brown) and 6) polyimide(brown). PCB substrate 1 is commercially available from MMC Americas,Inc., Rolling Meadows, Ill. PCB substrates 2, 3, 4, and 5 arecommercially available from TRC Circuits, Inc., Minneapolis, Minn. PCBsubstrate 6 is commercially available from 3M, St. Paul, Minn. The PCB'sranged in thickness from approximately 1 to about 2 mm. Eachphotopolymerizable composition was evaluated for photocuring with eachcuring light and each PCB material according to following procedure: Onedrop of the photopolymerizable composition was applied to a thin film ofpolyester which was placed directly on the PCB. The light guide of eachrespective light source was placed in direct contact with the PCB on theside directly opposite the drop of adhesive. The light was activated forapproximately 20 seconds. Following the light exposure, the compositionwas examined and the physical state established as uncured (NC), slightgel (some solid formed in liquid), soft gel (soft solid formed), gelled(solid formed), or cured (hard solid formed). The results are compiledin Table 2C, below.

Total Light Transmission, Spectra of Various Printed Circuit Boards

Each printed circuit board material described above was evaluated fortotal light transmission from 200-2500 nm according to the followingprocedure: All measurements were made on a Perkin Elmer Lambda 19Spectrophotometer fitted with an RSA-PE-19a integrating sphere accessory(Perkin Elmer Corp., Norwalk, Conn.). The sphere was 150 mm (6 inches)in diameter and complied with ASTM methods, e.g., D1003-97, and E308-96,as published in ASTM Standards on Color and Appearance Measurement,Third Edition, ASTM, West Conshohocken, Pa., 1991. The instrument waszeroed against air with a white plate in the rear sample position. Amask with a window of 0.32 cm×1.6 cm was placed directly in front ofeach circuit board sample. Set out below in Table 2B are the significanttransmission wavelengths for each of the printed circuit board materialsevaluated.

TABLE 2B Useful Visible Light Transmission Wavelengths SubstrateMaterial Observed Color (nm) 1) alumina (white) >400 nm 2) FR4 epoxy(yellow) >400 nm 3) FR4 epoxy + green (green) 475-575, >650 nm soldermask 4) FR0406 epoxy (yellow) >475 nm 5) BT-epoxy (brown) >525 nm 6)polyimide (brown) >525 nm

TABLE 2C Irradiation Photopolymerizable Compositions Through VariousPrinted Circuit Board Materials with Three Light Sources Light SourcesEFOS ™ UV/VIS Med. Pressure Hg Arc 254, 313, 365, Initiator System 405,430, 530, 3M Dental Light Tungsten Absorption Printed Circuit 545, 575,590, GE Light Engine ™ Halogen Compounds Wavelengths Board Material 610nm Visible 380-700 nm 400-500 nm Photopolymerization (20 seconds or lessexposure) IRGACURE ™ 254-365 nm None <2 sec   NC^((e)) NC 184 (3%)(comparative) alumina Cured^((a)) NC NC FR4 epoxy (no NC NC NC mask) FR4epoxy NC NC NC (green mask) FR0406 epoxy NC NC NC BT-epoxy NC NC NCpolyimide NC NC NC IRGACURE ™ 254-360 nm None <2 sec 5 sec NC 500 (3%)soft gel^((c)) (comparative) alumina soft gel slight gel^((d)) NC FR4epoxy (no NC NC NC mask FR4 epoxy NC NC NC (green mask) FR0406 epoxy NCNC NC BT-epoxy NC NC NC polyimide NC NC NC IRGACURE ™ 254-380 nm None <2sec 5 sec gel^((b)) NC 651 (3%) (comparative) alumina cured NC NC FR4epoxy (no NC NC NC mask FR4 epoxy NC NC NC (green mask) FR0406 epoxy NCNC NC BT-epoxy NC NC NC polyimide NC NC NC IRGACURE ™ 254-375 nm None <2sec 10 sec 20 sec soft gel 907 (3%) (comparative) alumina cured soft gelNC FR4 epoxy (no NC NC NC mask) FR4 epoxy NC NC NC (green mask) FR0406epoxy NC NC NC BT-epoxy NC NC NC polyimide NC NC NC IRGACURE ™ 254-425nm None <2 sec <2 sec <2 sec 369 (3%) alumina cured cured cured FR4epoxy (no cured cured cured mask) FR4 epoxy NC soft gel cured greenmask) FR0406 epoxy NC NC NC BT-epoxy NC NC NC polyimide NC NC NCIRGACURE ™ 254-425 nm None <2 sec <2 sec <2 sec 1700(3%) alumina curedcured cured FR4 epoxy (no cured cured cured mask) FR4 epoxy NC curedcured (green mask) FR0406 epoxy NC NC NC BT-epoxy NC NC NC polyimide NCNC NC Camphorquinone 400-500 nm None <2 sec <2 sec <2 sec (0.50%) Ethylalumina cured cured cured dimethylamino- benzoate (0.70%) Diphenyl FR4epoxy (no cured cured cured Iodonium PF₆ mask) (0.60%) FR4 epoxy curedcured cured (green mask) FR0406 epoxy soft gel cured cured BT-epoxy NCNC soft gel polyimide NC NC NC Rose Bengal 450-580 nm None <2 sec <2 sec<2 sec (0.15%) Ethyl alumina cured cured cured dimethylamino- benzoate(0.70%) Diphenyl FR4 epoxy (no cured cured cured Iodonium PF₆ mask)(0.60%) FR4 epoxy cured cured cured (green mask) FR0406 epoxy curedcured cured BT-epoxy soft gel cured cured (bottom only) polyimide softgel cured NC Toluidine Blue O 450-690 nm None cured cured gelled (0.10%)Ethyl alumina gelled cured NC dimethylamino- benzoate (0.50%) DiphenylFR4 epoxy (no gelled cured NC Iodonium PF₆ mask) (0.50%) FR4 epoxygelled cured NC (green mask) BT-epoxy gelled cured NC polyimide gelledcured NC Methylene Blue 500-700 nm None cured cured NC (0.10%) Ethylalumina gelled gelled NC dimethylamino- benzoate (0.50%) Diphenyl FR4epoxy (no NC gelled NC Iodonium PF₆ mask) (0.50%) FR4 epoxy gelled curedNC (green mask) BT-epoxy NC gelled NC polyimide gelled cured NC^((a))cured = hard solid formed ^((b))gelled = solid formed ^((c))softgel = soft solid formed ^((d))slight gel = some solid formed in liquid^((e))NC = not cured

The data of Table 2C illustrate that successful photocuring ofcompositions through the printed circuit boards required three keyelements including: 1) identification of light transmissive spectralregions associated with the various substrates; 2) identification ofphotoinitiators that absorbed light at the transmission wavelengths ofthe substrate; and 3) selection of a light source that provided actinicradiation at wavelengths that were readily transmitted through thesubstrate and were absorbed by the photoinitiator. Successfulphotopolymerization through most PCB's required wavelengths of lightbeyond the UV portion of the electromagnetic spectrum, i.e., greaterthan 400 nm.

Example 3

Several adhesive liquids and films were prepared as described below:

Adhesive films:

Sample 3-A

A 7 g sample of acrylated epoxy CN™ 104 (Sartomer Co., Inc., Exton, Pa.)was combined with 10.5 g of a solution (28.6%w/w in tetrahydrofuran(THF)) of powdered phenoxy resin PKHP (Phenoxy Associates, Rock Hill,S.C.). A clear solution was obtained. To this solution, camphorquinone(0.05 g), Ph₂ISbF₆ (0.05 g) and EDMAB (0.05 g) were added. The solutionwas coated at 0.15 mm (6 mil) on a silicone treated poly(ethyleneterephthalate) (PET) release liner, such as is commercially availablefrom Courtalds Aerospace, Inc.; Glendale, Calif., then allowed to airdry. All coating and drying was performed under yellow lights.

Sample 3-B

A 7 g sample of tris(hydroxyethyl)isocyanurate triacrylate (SR368™,Sartomer Co., Inc.) was combined with 10 g of a solution (30%w/w in THF)of bisphenol Z-type polycarbonate (TS2020™, Teijin Chemicals, Ltd.,Tokyo, JP). Bisphenol Z is 1,1-bis(4-hydroxyphenyl)cyclohexane. A clearsolution was obtained. The same catalysts and amounts were added asdescribed for Sample 3-A above. Coating was also as described above.

Liquid adhesives:

Sample 3-C

To 1.25 g of a solution (40% in THF) of polyetherimide oligomer(ULTEM™,GE Plastics Div., GE Company, Pittsfield, Mass.) was added 9.5 gof 3,4-epoxycyclohexylmethyl-3,4-epoxycyclohexanecarboxylate (ERL™ 4221,Union Carbide Corp., Danbury, Conn.). The sample was shaken untilhomogeneous. The resulting solution was charged with 0.10 g oforganometallic photoinitiator (antimony pentafluoride salt ofcyclopentadienyl iron xylenes, CpFeXySbF₆, 3M). The solution was pouredinto small aluminum pans to allow the solvent to evaporate. A clearliquid was obtained, and protected from light.

Additional liquid adhesive 3-D and 3-E, having formulations shown inTable 3A, were prepared by mixing the ingredients as shown.

TABLE 3A Adhesive Compositions 3-D (parts 3-E (parts Component byweight) by weight) Bis(glycidyl methacrylate) (Bis GMA) 22.50 12.50Triethyleneglycol dimethacrylate (TEGDMA) 02.50 12.50 Camphorquinone(CPQ) 00.12 00.17 Ethyl p-dimethylaminobenzoate (EDMAB) 00.12 01.00Diphenyl iodonium hexafluorophosphate 00.12 00.60 Rose Bengal (RB)00.012 00.10 R976 fumed silica 00.00 03.50

Curing of Adhesives:

Procedure 1

Adhesives 3-A, 3-B, and 3-C were used to mount silica chips to aluminaand FR4 circuit boards having a solder mask. In the case of filmadhesives, the adhesive was laminated onto the chip or the circuitboard. For the liquid adhesive, a small drop was placed on the board andused to hold the chip in place. For curing the adhesives, all sampleswere placed on a hot plate with the temperature set to 180° C. with thechip in direct contact with the hot plate. Additional chips were used asspacers around the periphery of the board. The adhesive was irradiatedthrough the circuit board for 20 sec with a 3M XL3000 dental curinglight with a light output between 400 and 500 nm. All adhesives cured tohard materials and the chips could not be removed when pried withtweezers.

Procedure 2

Compositions 3-A, 3-D and 3-E were evaluated as possible adhesives formounting silica chips to FR4 circuit boards according to the followingprocedure: A silica chip was placed in contact with a metal plate heatedat 180° C. for approximately 30 seconds. The FR4 PCB was held by vacuumto a transparent quartz plate. The liquid resin or thermoplastic filmwas applied to the PCB, and the l° C.B and chip brought together under207 KPa (30 psi) pressure for about 10 seconds then irradiated throughthe quartz plate with a 3M XL3000 Dental curing light for 20 to 30seconds. The vacuum was removed, releasing the PCB and silica chip. As acomparative, the trial was repeated without exposure to light. Allsamples were evaluated with tweezers and determined to be eitherwell-adhered (“good adhesion”) or easily removed (“poor adhesion”).Results are shown in Table 3B, below:

TABLE 3B Sample Light exposure No light exposure 3A well-cured/goodadhesion no-cure/poor adhesion 3D well-cured/good adhesion no-cure/pooradhesion 3E well-cured/good adhesion no-cure/poor adhesion

The data clearly show that chips can be effectively bonded to printedcircuit boards via light exposure through the circuit board surfaceopposite to the chip/PCB interface. In the absence of light exposure theadhesive compositions remained uncured, therefore providing thepossibility of soldering without premature polymerization. Both filmsand liquid compositions (including cationically and/or free radicallycurable systems) were effective.

Example 4 Photolaminating Compact Discs

Two metallized polycarbonate halves of a Compact Disc (CD), each with anoptical density of about 2.5, were photolaminated to one anotheraccording to the following method:

A thin film of the adhesive according to the formulations shown below inTable 4 was applied to the metallic side of one disc, followed byplacement of the metallic side of a second disc in contact with thecoated adhesive. Slight pressure was applied to the sandwichedconstruction to provide a thin and relatively even adhesive layer. Thesamples were then placed on a standard radiation processing line at adistance slightly beyond the manufacturer's recommended exposuredistance using a Fusion Q bulb (Fusion UV Systems, Inc., Gaithersburg,Md.) that provided an output of about 2.6 watts/cm² (between 400 and 500nm) at a line speed of about 2.4 m/minute. This provided a residencetime under the light of about 0.6 seconds and a dosage of 2.6 J/cm². Theresulting samples were well adhered and attempts to separate themresulted in delamination of the metallic coating from the polycarbonatedisc. The ability to rapidly photolaminate through reflective substratesusing this approach was thus confirmed. The two adhesive formulationsevaluated for DVD use are shown below. These materials absorbed visiblelight between 400-500 nm and were well matched with the Fusion Q bulb.This method provided a rapid and simple process for laminating a varietyof reflective substrates including DVD-RAMs, DVDs, CD's, etc.

TABLE 4 Component Parts by weight Adhesive 1 UV-6100B/HPA DVD 50.00Adhesive Camphorquinone 0.50 Ethyl p- 0.35 dimethylaminobenzoateAdhesive 2 UV-6100B/HPA DVD 50.00 Adhesive Camphorquinone 0.50 Ethyl p-0.25 dimethylaminobenzoate Diphenyl iodonium 0.50 hexafluorophosphate

UV6100B is a urethane diacrylate monomer available from Nippon GoseiKagaku (Nippon Synthetic Chemical Industry, Inc., Osaka, JP).

HPA is hydroxypropyl acrylate monomer available from Rohm Tech Inc.,Malden. Mass.

Example 5 Photolaminating Reflective Films Using a Cationically CurableEpoxy Composition

Two highly reflective metallized sputtered aluminum PET films, each withan optical density of about 2.5, were photolaminated to one another witha photocurable epoxy composition according to the following method:

A thin film of a liquid epoxy adhesive (formulation shown in Table 5,below) was applied to the metallic side of a 2.5 cm×2.5 cm sample ofsputtered aluminum-coated PET film, followed by placement of themetallic side of a similar 2.5 cm×2.5 cm square of aluminized PET filmin contact with the coated adhesive. Slight pressure was applied to thesandwiched construction to provide a thin and relatively even adhesivelayer. The sample was directly contacted and irradiated for 60 secondswith the light guide (12 mm diameter) of a 3M XL-3000 dental curinglight, which provided approximately 500 mw/cm² of blue light having awavelength between 400 and 500 nm. The sample was examined 30 minuteslater and was observed to be well cured and adhered only in the regionplaced directly beneath the light. The remainder of the epoxycomposition was uncured. This example confirms that reflectivesubstrates were rapidly photolaminated with a photocurable epoxy vialight exposure through highly reflective aluminized PET films.

TABLE 5 Adhesive Composition Component Parts by weight ERL 4221E Epoxy9.50 p-THF 250 diol 0.50 Camphorquinone 0.10 Ethyl p- 0.01dimethylaminobenzoate Dodecyl diaryl 0.15 iodonium methide

ERL 4221E is a cycloaliphatic diepoxide available from Union Carbide.

Dodecyl diaryl iodonium methide is bis(dodecylphenyl)iodoniumtris(tifluoromethylsulfonyl)methide, prepared as described in Example 2of U.S. Pat. No. 5,554,664, incorporated herein by reference.

Example 6 Photolaminating Reflective and Colored Multilayered Films

Two highly reflective (non-metallized) multi-layered films, each with anoptical density of about 2.5, were photolaminated to one another with avisible light photocurable methacrylate composition according to thefollowing method:

A thin film of a methacrylate adhesive (formulation below) was appliedto one side of a 5 cm×5 cm multi-layered reflective film, described inExample 1 of U.S. patent application Ser. No. 09/126,917, which isincorporated herein by reference, followed by placement of a similar 5cm×5 cm square multilayered reflective film in contact with the coatedadhesive. Slight pressure was applied to the sandwiched construction toprovide a thin and relatively even adhesive layer. The sample wasdirectly contacted and irradiated for 10 seconds with the light guide(12 mm diameter) of a 3M XL-3000 dental curing light which providedapproximately 500 mw/cm² of blue light having a wavelength between 400and 500 nm. The sample was examined immediately and observed to be wellcured and adhered in the region placed directly beneath the light. Mostof the remaining methacrylate was uncured. This confirms that reflectivemultilayer films were rapidly photolaminated with a photocurablecomposition via light exposure through highly reflective multilayerfilms. This approach provides a rapid and simple process for laminatinga variety of reflective and colored multilayered films.

TABLE 6 Adhesive Formulation Component Parts by weight Bis GMA 5.00TEGDMA 5.00 Camphorquinone 0.02 Ethyl p- 0.10 dimethylaminobenzoateDiphenyliodonium 0.06 hexafluorophosphate

Example 7 Underfilled Electronic Device (Acrylate Adhesive)

A black, opaque electronic chip was soldered in place on a 1.5 mm thickFR4 printed circuit board having metallic contacts thereon, and coatedon both sides with a solder mask. A space of approximately 0.10 mmremained between the top of the PCB mask and the soldered chip. Thisassembly was placed on a hot plate at 100° C. for approximately oneminute, then a drop of a red-colored acrylate adhesive formulationdescribed above as Example 1B in Table 1 was placed on one side of thesoldered chip, at the interface of the board and the chip. The adhesiveformulation wicked under the chip in about 5 seconds. The assembly wasremoved from the hot plate and immediately subjected to irradiation by aXL-3000 blue dental light (3M) through the FR4 board from the sideopposite the soldered chip. The adhesive was observed to solidifyrapidly and change from red to colorless in less than 20 seconds.

Example 8 Underfilled Electronic Device (Acrylate Adhesive)

The procedure of Example 7 was repeated except that the circuit boardwith soldered chip was not heated prior to application of the adhesive.The adhesive formulation required approximately two minutes to wickunder the chip at 23° C. When the adhesive had wicked under the chip,the assembly was heated on a hot plate at 100° C. for 20 seconds,whereupon the adhesive formed a bead around all sides of the chip. Theassembly was removed from the hot plate and immediately exposed to lightas described in Example 7 for 20 seconds, at which time the adhesive wascured.

Example 9 Underfilled Electronic Device (Epoxy Adhesive)

The procedure of Example 7 was repeated except that an epoxy adhesiveformulation, shown in Table 5, above, was used in place of an acrylateadhesive. The epoxy adhesive wicked under the chip in about 5 seconds.The assembly was removed from the hot plate and immediately subjected toirradiation by a XL-3000 blue dental light (3M) through the FR4 boardfrom the side opposite the soldered chip. The adhesive was observed tosolidify rapidly and change from red to colorless in less than 20seconds.

Example 10 Underfilled Electronic Device (Filled Acrylate Adhesive)

The procedure of Example 7 was repeated except that the acrylateadhesive was modified by addition of a filler prior to applying theadhesive to the chip-board interface. An amorphous spherical silicapowder having an average particle size of approximately 5 microns(SILSTAR™ LE-05, Nippon Synthetic Chemical Industry Co., Ltd. Tokyo, JP)was added in the amount of 1.44 g filler per g of acrylate adhesive toachieve a loading of 65% by weight. The filled adhesive was dispensedalong one side of the heated chip assembly. After two minutes on the hotplate, there was no evidence of any fillet formation on the sideopposite from where the adhesive was dispensed. The adhesive was curedusing the XL-3000 blue dental light, after which the chip was de-bondedfrom the board for examination. Approximately 90% of the area under thechip had been encapsulated, and the adhesive appeared to be fully cured.

Example 11 Underfilled Electronic Device (Filled Epoxy Adhesive)

The procedure of Example 10 was repeated except that the acrylateadhesive was replaced by the epoxy adhesive as described in Example 9.The amorphous silica filler was used at 65% by weight loading. After twominutes on the hot plate, there was no adhesive formulation seen on theside opposite from where the adhesive was dispensed. Subsequently, thedispensed adhesive was cured in the same manner as described in example7, after which the chip was de-bonded from the board for examination.Approximately 90% of the area under the chip had been encapsulated, andthe adhesive appeared to be fully cured.

Various modifications and alterations that do not depart from the scopeand intent of this invention will become apparent to those skilled inthe art. This invention is not to be unduly limited to the illustrativeembodiments set forth herein.

What is claimed is:
 1. A method for preparing a soldered and underfilledflip chip assembly on a circuit substrate, the method comprising thesteps of: a) providing 1) an integrated circuit chip having a surfacecomprising reflowable solder bumps with contact tips thereon, and 2) aprinted circuit substrate having a bonding site, wherein at least one ofsaid chip and said circuit substrate is transmissive to actinicradiation in an identified spectral region having wavelengths greaterthan 400 nm and up to 1200 nm, b) applying a photopolymerizable adhesivecomposition directly to one or both of the surface of the chip withsolder bumps and the bonding site of the printed circuit substrate, saidmethod providing exposure of said contact tips of said solder bumps ofsaid chip, said photopolymerizable adhesive composition comprising aphotopolymerizable moiety and a photoinitiator therefor, wherein saidphotopolymerizable composition absorbs radiation in said identifiedspectral region of said radiation transmissive chip or circuitsubstrate, c) aligning and pressing the exposed tips of the bumps on thesurface of said chip against the bonding site of said circuit substrate,d) subjecting the flip chip assembly to heat at a temperature sufficientto melt and reflow the solder so as to establish electrical contact anda metallurgical bond between said chip and said circuit substrate,wherein the photopolymerizable material remains substantially uncured,and e) directing radiation within said identified spectral regionthrough said radiation transmissive chip or circuit substrate for a timesufficient to cure said photopolymerizable adhesive composition and toproduce said soldered and underfilled flip chip assembly on said circuitsubstrate.
 2. The method according to claim 1 further comprisingconducting a functional evaluation of the soldered electricalconnections prior to performing radiation step e).
 3. The methodaccording to claim 2 further comprising performing steps of i) removingthe chip from the circuit substrate if the functional evaluation showsinsufficient electrical contact therebetween, and ii) cleaning the chipand the bonding site of the circuit substrate and repeating steps a)through e).
 4. The method according to claim 1 wherein one or both ofsaid chip and said circuit substrate is opaque.
 5. The method accordingto claim 4 wherein said cure of said photopolymerizable adhesivecomposition takes place in a time period in the range of more than zeroseconds to less than 2 minutes.
 6. The method according to claim 1wherein one or both of said chip and said circuit substrate is colored.7. The method according to claim 1 wherein one or both of said chip andcircuit substrate is selected from the group consisting of alumina andpolyimide substrates.
 8. The method according to claim 1 wherein saidcircuit substrate is selected from the group consisting of FR4, FR0406,and BT epoxy substrates.
 9. The method according to claim 1 wherein thetemperature of the flip chip assembly in step d) is up to about 220degrees C.